Help needed with mysterious stalling issue

EJD

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Ok, so i've had a few issues stalling lately (mainly while driving) and I feel I have actually corrected the "while driving" issues by replacing old parts and some great insight from the forum, i'm wondering if my current stalling issue is more specific now and if any of you have any ideas or suggestions on this since I feel like I can narrow it down to 3 specific scenarios that I have stalled in.

1. Going from reverse into drive. Just about every time on a cold start I shift from park into reverse, back up, depress and hold the brake pedal...the moment it is shifted into drive (a sputter stall occurs). I do not even have to let go of the brakes before it stalls, and if I do the whole motion quickly and hit the gas pedal fast before or as its stalling it will stay alive and actually drive forward without totally stalling...but its weird to have to do that. Lol.

2. While idling at a red light. Brake pedal depressed, and after a minute or so it feels like it just chokes and stalls, but always starts right back up. If I pull up to a red light and shift into "park" at the stop light instead of holding the brakes, it does NOT stall out. Interesting...right? I notice I idle higher while in park vs in drive.

3. Making a hard stop. Pulled up to a crossroad a little hot once and realized there was a stop sign. No skidding but it did stall out when I came to a full stop there...

The common denominator is the brakes in all scenarios. So I'm curious to know if there is any connection between the hitting or holding the brakes and stalling that anyone knows of?

Please reply if anything seems to make sense as to what is going on here. I am determined to figure this stalling thing out and I know of at least one other forum member that is having the same issue going on too.

Thank you in advance!
 
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I had some very strange stalling issues recently and it ended up being a bad throttle position sensor. Because it happened so quickly and intermittently the codes weren't being stored in the computer. For eight months and 6 mechanics I chased that gremlin until it finally acted up badly enough and long enough at a shop for them to catch the code. I had issues from stalling at a stop to stalling at 60 mph and everything in between... And if you're capable of replacing it yourself it may be worth a shot. Only $300 to have it replaced by the shop.
 
I had some very strange stalling issues recently and it ended up being a bad throttle position sensor. Because it happened so quickly and intermittently the codes weren't being stored in the computer. For eight months and 6 mechanics I chased that gremlin until it finally acted up badly enough and long enough at a shop for them to catch the code. I had issues from stalling at a stop to stalling at 60 mph and everything in between... And if you're capable of replacing it yourself it may be worth a shot. Only $300 to have it replaced by the shop.

She makes a very good point. Her symptoms (which I followed for months) sound similar to yours. In addition to that, she was never throwing any codes, which made it nearly impossibly to diagnose. This may be worth looking into.
 
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I'll have to look into the tps - have had an occasional stalling issue, maybe 1-2x a month. When it happens its almost always when backing into my driveway or backing into a parking spot at work - the common denominator seems to be reversing while turning...
 
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Ok, so i've had a few issues stalling lately (mainly while driving) and I feel I have actually corrected the "while driving" issues by replacing old parts and some great insight from the forum, i'm wondering if my current stalling issue is more specific now and if any of you have any ideas or suggestions on this since I feel like I can narrow it down to 3 specific scenarios that I have stalled in.

1. Going from reverse into drive. Just about every time on a cold start I shift from park into reverse, back up, depress and hold the brake pedal...the moment it is shifted into drive (a sputter stall occurs). I do not even have to let go of the brakes before it stalls, and if I do the whole motion quickly and hit the gas pedal fast before or as its stalling it will stay alive and actually drive forward without totally stalling...but its weird to have to do that. Lol.

2. While idling at a red light. Brake pedal depressed, and after a minute or so it feels like it just chokes and stalls, but always starts right back up. If I pull up to a red light and shift into "park" at the stop light instead of holding the brakes, it does NOT stall out. Interesting...right? I notice I idle higher while in park vs in drive.

3. Making a hard stop. Pulled up to a crossroad a little hot once and realized there was a stop sign. No skidding but it did stall out when I came to a full stop there...

The common denominator is the brakes in all scenarios. So I'm curious to know if there is any connection between the hitting or holding the brakes and stalling that anyone knows of?

Please reply if anything seems to make sense as to what is going on here. I am determined to figure this stalling thing out and I know of at least one other forum member that is having the same issue going on too.

Thank you in advance!

It sounds like you may have an internal vacuum leak inside your power brake booster.
I wouldn't drive it on the road to try the following test : Disconnect your big vacuum line at the booster and plug the line securely in some way. Start the Jeep and see if the problem goes away. If it does, the booster is bad.

While your at it, check for any other possible vacuum leaks on the engine. There may be numerous additional small leaks that are accumulative and add up.
 
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To me, it sounds like your autobox is not slipping when it should be. If your revs drop by a noticable amount when you shift into gear.... drive or reverse, then the gearbox is loading the engine. Maybe too much for a cold engine which is when it is likely to drag more. Time to change the gearbox oil, maybe?
 
I had some very strange stalling issues recently and it ended up being a bad throttle position sensor. Because it happened so quickly and intermittently the codes weren't being stored in the computer. For eight months and 6 mechanics I chased that gremlin until it finally acted up badly enough and long enough at a shop for them to catch the code. I had issues from stalling at a stop to stalling at 60 mph and everything in between... And if you're capable of replacing it yourself it may be worth a shot. Only $300 to have it replaced by the shop.
I appreciate that but i've already done that and much much more.

The other thing two mechanically inclined folks suggested was the idle air intake valve...
In the past month I have replaced myself the IAC valve, the MAP sensor, the TPS sensor, the Crankshaft Position sensor, the Camshaft position sensor, all 4 O2 sensors, and most recently have installed a new Fuel Pump assembly. The issues still persist and its not throwing any codes or check engine lights...which is kind of blowing my mind a little.

It sounds like you may have an internal vacuum leak inside your power brake booster. I wouldn't drive it on the road to try the following test : Disconnect your big vacuum line at the booster and plug the line securely in some way. Start the Jeep and see if the problem goes away. If it does, the booster is bad. While your at it, check for any other possible vacuum leaks on the engine. There may be numerous additional small leaks that are accumulative and add up.
Vacuum stuff is next in line, anyone have a diagram of where the lines are and/or how many i'm supposed to be looking for? I need a video or something of that test your speaking of, i'm a noob to most of this stuff but have the means and ambition to potentially make it happen.

To me, it sounds like your autobox is not slipping when it should be. If your revs drop by a noticable amount when you shift into gear....drive or reverse, then the gearbox is loading the engine. Maybe too much for a cold engine which is when it is likely to drag more. Time to change the gearbox oil, maybe?
I've been told changing the transmission fluid was not a good idea on a vehicle with as many miles as I have if there is no record of it being done before. I'm open to just about anything and was going to do this but I have been advised against it by more than one mechanic. To me it makes no sense. Could the transmission fluid being overfilled have any of these weird symptoms? When I check the fluid it looks good and is the right color but is actually filled above the "max" fill line by a 1/2" or so.

Also, how would this explain the stalling while idling at a stop light for example?
 
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I appreciate that but i've already done that and much much more.

In the past month I have replaced myself the IAC valve, the MAP sensor, the TPS sensor, the Crankshaft Position sensor, the Camshaft position sensor, all 4 O2 sensors, and most recently have installed a new Fuel Pump assembly. The issues still persist and its not throwing any codes or check engine lights...which is kind of blowing my mind a little.

Vacuum stuff is next in line, anyone have a diagram of where the lines are and/or how many i'm supposed to be looking for? I need a video or something of that test your speaking of, i'm a noob to most of this stuff but have the means and ambition to potentially make it happen.

I've been told changing the transmission fluid was not a good idea on a vehicle with as many miles as I have if there is no record of it being done before. I'm open to just about anything and was going to do this but I have been advised against it by more than one mechanic. To me it makes no sense. Could the transmission fluid being overfilled have any of these weird symptoms? When I check the fluid it looks good and is the right color but is actually filled above the "max" fill line by a 1/2" or so.

Also, how would this explain the stalling while idling at a stop light for example?


I've posted a link to a video that includes a demonstration of the location of a jeep brake booster vacuum line, and how to disconnect it to enable you to do your test. It just pulls off, and may or may not have a small clamp securing it. Once disconnected, you simply need to plug the end of the line with something, then start up the engine and see if the stalling problem goes away when pressing the brake pedal and shifting into reverse etc..

DONT drive the vehicle this way, as you will no longer have power assist on your brakes, and the pedal effort will be different.

You can disregard the other parts of the video as you are not replacing your booster but simply troubleshooting.
If the problem does go away, it's ether the little plastic fitting that the hose plugs onto, which is also a one-way check valve which is replaceable, or the booster internal rubber diaphragm and seals could be bad.


Here is another video showing the vacuum line you'll need to remove and plug for testing:

 
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I've been told changing the transmission fluid was not a good idea on a vehicle with as many miles as I have
This is rediculous advice. How can changing oil be bad for a transmision, as opposed to running 20 year old oil ??
My brother in law owns a gearbox shop, and regularly flushes auto transmissions. Older trans should also still have removable filters, but I don't know enough about the jeeps to be certain of that.
The reason the gearbox COULD be the cause of the stall, is the way that autos engage drive, using hydraulics to clamp steel bands around the required drive shaft, thereby selecting the gear. if the release gallery is clogged, or the band is dragging, drive is engaged while you're sitting with your foot on the brake (and in drive).. too much drag, you stall. if you can sit at the lights in neutral,or park and it doesn't stall, and your revs increase, then this is an indication of the drive engaging too much at idle. Your torque converter should compensate for some drag, but too much will stall the engine. Old oil, or the wrong grade, will increase drag. Burnt oil is the worst, as the carbon particals will act as an abrasive as well as clogging ports and valves. Oil can be burnt by towing or otherwise overheating the trans. All oil needs to be changed sometime, as it will have a limited life. constant heating and cooling, condensation, contamination will degrade any oils performaance over time. And autos need servicing just like any other mechanical item.
 
3. Making a hard stop. Pulled up to a crossroad a little hot once and realized there was a stop sign. No skidding but it did stall out when I came to a full stop there...

This is the prefect indicator of a gearbox problem. emergency stop, stall. the gearbox did not disengage the engine from the wheels quickly enough to prevent the engine stall.

A question for you. If you sit with the brakes on, in drive on flat ground, then release the brakes without touching the gas, how readily does the jeep move off, if at all? I would expect slow creep at best. very light brake should stop it. any more than that indicated too much drag, or too high an idle speed.. Idle should be 800 - 900 rpm
 
Once disconnected, you simply need to plug the end of the line with something, then start up the engine and see if the stalling problem goes away when pressing the brake pedal and shifting into reverse etc.
Ok so I pulled the hose off, plugged it with a Sharpie (it was a perfect fit), and started it up, shifted into reverse, then drive, drove down an empty street, then reversed all the way back to my driveway, parked and it was fine. No stalls, nothing!
However it doesn't happen 100% of the time either, but this does make me very curious now about this, and I will try this later tonight after it sits for 12 hours and on a cold start when it almost always happens. (Then I plugged the hose back in, went to the store and it sputter stalled as I was pulling into a parking spot). The more I look into the Brake Booster now, it seems I have other symptoms of the diaphragm inside failing.
I've been told changing the transmission fluid was not a good idea on a vehicle with as many miles as I have
This is rediculous advice. How can changing oil be bad for a transmision, as opposed to running 20 year old oil ??
Apparently it is a widely spread notion that changing automatic transmission oil in such conditions will cause the automatic transmission to fail because the fluid that has been in the transmission for a long time has become dirty and gritty. According to this notion, this gritty fluid is actually providing needed friction for the worn internal components of the transmission. Therefore, changing the fluid would remove this added friction supplement that the internal transmission parts now need to operate properly, which would cause the transmission to slip or suffer some type of catastrophic failure.
A question for you. If you sit with the brakes on, in drive on flat ground, then release the brakes without touching the gas, how readily does the jeep move off, if at all? I would expect slow creep at best. very light brake should stop it. any more than that indicated too much drag, or too high an idle speed.. Idle should be 800 - 900 rpm
Ok, so flat ground (tons of that in Florida, lol) in drive, foot off brake and coasting, initial idle starts off at 500-600rpms and a slow creep of about 5mph...but momentarily does raise up to 800-900rpms and coasts steadily at 8.5mph with my GPS.
 
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Apparently it is a widely spread notion that changing automatic transmission oil in such conditions will cause the automatic transmission to fail because the fluid that has been in the transmission for a long time has become dirty and gritty. According to this notion, this gritty fluid is actually providing needed friction for the worn internal components of the transmission. Therefore, changing the fluid would remove this added friction supplement that the internal transmission parts now need to operate properly, which would cause the transmission to slip or suffer some type of catastrophic failure.
Nothing could be more untrue than that old wive's tale.

If a transmission coincidentally failed after its ATF was changed, two likely scenarios are at play here... 1) The ATF was changed out of desperation, the transmission was not shifting properly so it was already in bad shape to begin with. 2) The transmission was about to fail anyway.
 
Nothing could be more untrue than that old wive's tale.

If a transmission coincidentally failed after its ATF was changed, two likely scenarios are at play here... 1) The ATF was changed out of desperation, the transmission was not shifting properly so it was already in bad shape to begin with. 2) The transmission was about to fail anyway.
I mean that does sound very logical, and I agree with you Jerry. I was only answering Andy P's question and stating that I have been advised against it several times from different mechanics, and don't really know who or what to believe since I am not one and am new to doing my own maintenance.

Trying to learn as I go...I mean I 've changed every other possible fluid in my Jeep except this one.

Do you believe I should change it out as it may be a contributing factor to my stalling issue?
Or do you think I should explore the Brake Booster/Vacuum Line route further?
 
Ok so I pulled the hose off, plugged it with a Sharpie (it was a perfect fit), and started it up, shifted into reverse, then drive, drove down an empty street, then reversed all the way back to my driveway, parked and it was fine. No stalls, nothing!
However it doesn't happen 100% of the time either, but this does make me very curious now about this, and I will try this later tonight after it sits for 12 hours and on a cold start when it almost always happens. (Then I plugged the hose back in, went to the store and it sputter stalled as I was pulling into a parking spot). The more I look into the Brake Booster now, it seems I have other symptoms of the diaphragm inside failing.
Apparently it is a widely spread notion that changing automatic transmission oil in such conditions will cause the automatic transmission to fail because the fluid that has been in the transmission for a long time has become dirty and gritty. According to this notion, this gritty fluid is actually providing needed friction for the worn internal components of the transmission. Therefore, changing the fluid would remove this added friction supplement that the internal transmission parts now need to operate properly, which would cause the transmission to slip or suffer some type of catastrophic failure.
Ok, so flat ground (tons of that in Florida, lol) in drive, foot off brake and coasting, initial idle starts off at 500-600rpms and a slow creep of about 5mph...but momentarily does raise up to 800-900rpms and coasts steadily at 8.5mph with my GPS.

Did you attempt your test again after sitting, and cold?
Make sure none of your other vacuum hose connections are loose as well, as your engine can only pull a set amount of vacuum at idle when you are experiencing this problem. Several smaller leaks can dump off enough vacuum to possibly cause stalling once your booster takes the Lion's share of it. The booster is the biggest vacuum consumer of all the engines accessories, and if you are already missing some via other leaks, It'll be more noticeable during braking.

On the driver's side of the intake manifold, below the level of your throttle body are several hose connections right next to each other, & sticking out horizontally towards the left fender area that you'll need to check.
Just because you see they're still plugged-on doesn't necessarily mean they are tight. You'll need to wiggle them around to make sure. They can sometimes swell up on the end and become loose. Make sure the two CCV (Crank Case Ventilation) lines running to your valve cover are secure as well. Put clamps on them if you have to, or even use plastic tie-wraps or Wire-Ties as some people call them. If you do find a swollen end on one of your rubber vacuum hoses, you may even need to cut off that small end piece before plugging it back on.

A failing booster can sometimes make a hissing sound and you can possibly hear it by starting the engine and listening under your dash as you press the pedal and the damaged rubber diaphragm changes shape.

Ok, enough of my incessant keyboard usage for now. Keep us updated...
 
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Did you attempt your test again after sitting, and cold?
Make sure none of your other vacuum hose connections are loose as well, as your engine can only pull a set amount of vacuum at idle when you are experiencing this problem. Several smaller leaks can dump off enough vacuum to possibly cause stalling once your booster takes the Lion's share of it. The booster is the biggest vacuum consumer of all the engines accessories, and if you are already missing some via other leaks, It'll be more noticeable during braking.

On the driver's side of the intake manifold, below the level of your throttle body are several hose connections right next to each other, & sticking out horizontally towards the left fender area that you'll need to check.
Just because you see they're still plugged-on doesn't necessarily mean they are tight. You'll need to wiggle them around to make sure. They can sometimes swell up on the end and become loose. Make sure the two CCV (Crank Case Ventilation) lines running to your valve cover are secure as well. Put clamps on them if you have to, or even use plastic tie-wraps or Wire-Ties as some people call them. If you do find a swollen end on one of your rubber vacuum hoses, you may even need to cut off that small end piece before plugging it back on.

A failing booster can sometimes make a hissing sound and you can possibly hear it by starting the engine and listening under your dash as you press the pedal and the damaged rubber diaphragm changes shape.

Ok, enough of my incessant keyboard usage for now. Keep us updated...
A longer sit/cold start attempt made just now as I was leaving work from a 12 hour shift at the hospital. I went out to the huge empty parking lot, no one at all there, dark still at 0430 and I popped the hood, pulled the BB hose, plugged it, and fired it up. I reversed back like normal (where I would normally stall every time), and it did not. Using the e-brake I stopped and put it in drive it also did not stall...I drove around the parking lot in a tiny area far away from anyone or anything and repeated the process a few time and it did not stall. However one time it sputtered and I felt some vibrations below as if it wanted to stall but didn't. Which is saying something, because thats exactly what it does when it stalls but it stay with me.

I then re-connected the hose and listened near the brake pedals and no constant hissing sound like in the video you posted but there is some air escaping when I depress the brake pedal. I also ran that test where you shut the Jeep off, pump the brakes 5-6 times to make the pedal feel firm and when you start the vehicle the brake pedal should drop from its position a little and it did not drop (which apparently is also a sign of a bad BB), also longer stop time from when you hit the brakes and where you actually stop.

I also just listened for any air leaks in the engine bay and its hard to hear any air hissing over the sound of a 4.0 to me, but I almost think I hear something leaking...hope its not all in my head. I did double check all those hoses you mentioned too under the TB on the side there and everything felt connected good there, but i'm not sure how many lines total there are or where they all go to, to check the other ends of them. I might attempt a smoke test at some point soon. I feel like were getting closer to the issue, but there may be multiple contributing factors in play here.

And thanks I appreciate the insight!
 
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A longer sit/cold start attempt made just now as I was leaving work from a 12 hour shift at the hospital. I went out to the huge empty parking lot, no one at all there, dark still at 0430 and I popped the hood, pulled the BB hose, plugged it, and fired it up. I reversed back like normal (where I would normally stall every time), and it did not. Using the e-brake I stopped and put it in drive it also did not stall...I drove around the parking lot in a tiny area far away from anyone or anything and repeated the process a few time and it did not stall. However one time it sputtered and I felt some vibrations below as if it wanted to stall but didn't. Which is saying something, because thats exactly what it does when it stalls but it stay with me.

I then re-connected the hose and listened near the brake pedals and no constant hissing sound like in the video you posted but there is some air escaping when I depress the brake pedal. I also ran that test where you shut the Jeep off, pump the brakes 5-6 times to make the pedal feel firm and when you start the vehicle the brake pedal should drop from its position a little and it did not drop (which apparently is also a sign of a bad BB), also longer stop time from when you hit the brakes and where you actually stop.

I also just listened for any air leaks in the engine bay and its hard to hear any air hissing over the sound of a 4.0 to me, but I almost think I hear something leaking...hope its not all in my head. I did double check all those hoses you mentioned too under the TB on the side there and everything felt connected good there, but i'm not sure how many lines total there are or where they all go to, to check the other ends of them. I might attempt a smoke test at some point soon. I feel like were getting closer to the issue, but there may be multiple contributing factors in play here.

And thanks I appreciate the insight!


One other suggestion would be to check your intake manifold bolts at the head to make sure none are loose, especially those on the rear of the engine that for some odd reason have been known to loosen up on the 4.0. You can develop a vacuum leak there as well.
 
Update!

Ok, so first I went on Ebay, bought a 2nd hand Mopar Brake Booster for $50 shipped from a TJ of a newer year and that had half the miles "my" TJ has and installed it. It had the same warped diaphragm and therefor the same vacuum leak and kept stalling upon idle with the brake pedal depressed. The good thing was the Ebay seller I bought through offered a money back guarantee if the product did not function. So I got my refund instantly and they didn't even want the product returned so I tossed it out.

Then, I went ahead and bought a fresh Mopar Brake Booster from the factory for $250 shipped, and just installed it this morning.
My stalling issue has gone away! I ran it through all of the 3 scenarios that made it stall before, and it did not stall out at all.

I am so very relieved right now, and I would love to thank the Forum here and everyone that schooled me along the way.
Thanks forum and thank you members, much appreciated!

Now I just need to figure out my leaky Throttle and TPS, and i'll be a happier camper.
 
Update!

Ok, so first I went on Ebay, bought a 2nd hand Mopar Brake Booster for $50 shipped from a TJ of a newer year and that had half the miles "my" TJ has and installed it. It had the same warped diaphragm and therefor the same vacuum leak and kept stalling upon idle with the brake pedal depressed. The good thing was the Ebay seller I bought through offered a money back guarantee if the product did not function. So I got my refund instantly and they didn't even want the product returned so I tossed it out.

Then, I went ahead and bought a fresh Mopar Brake Booster from the factory for $250 shipped, and just installed it this morning.
My stalling issue has gone away! I ran it through all of the 3 scenarios that made it stall before, and it did not stall out at all.

I am so very relieved right now, and I would love to thank the Forum here and everyone that schooled me along the way.
Thanks forum and thank you members, much appreciated!

Now I just need to figure out my leaky Throttle and TPS, and i'll be a happier camper.


Hey that's great news. Always nice to fix a frustrating problem like that.
Speaking of frustrating, I too had a problem with my throttle body that I couldn't solve until I replaced that throttle body.
My TJ had an idle speed of approximately 430-450rpm, and "shuddered" at stop lights with a periodic stall, followed by an IAC fault code. I repeatedly removed, cleaned, and in inspected and couldn't see ANY logical reason for the problem. All sensors were changed to MOPAR, and problem remained.

Someone in my family must have gotten tired of me bitchin about it, and shipped me an aftermarket throttle body that they bought on Amazon. It completely solved the problem and runs very smooth. Pricy though, around $270.00.
(BBK 1724 62mm Throttle Body - High Flow Power Plus Series for Jeep 4.0L)

If you aren't experiencing driveability issues, I wouldn't worry about the smoke test leakage on the throttle body. If you are,
you could try another used but stock throttle body first.

 
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