Super Annoying Rough Idle Issue (Can't Find Info On This Anywhere)

WPGB1977

WPGB1977

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North Carolina, United States
I have been chasing a rough idle issue for the past couple of months and it is killing me! I have researched this issue and have exhausted all of the threads and can't really get to a solution that doesn't require deep mechanical knowledge or a relatively large amount of money.

I have thrown the usual "easy" solutions at it - new plugs, cleaned IAC and throttle body, run fuel system cleaner through it - but to no avail.

Jeep isn't throwing any codes. Here's what's going on.

Symptom #1: Will idle roughly at a standstill. Barely perceptible but definitely there. Intermittently worse some times than others. Could just learn to live with this except for Symptom #2. See below.

Symptom #2: This is what is weird. After backing the Jeep into a parking spot or my garage, it really bogs down and threatens to quit. Sounds horrible and can't be good for it. After about 15 - 20 seconds of sounding like it's struggling to keep running, it goes back to idling *almost* normally much like it does in symptom #1. By the way, the extent of the struggling varies and I can't correlate it to any specific conditions (heat, length of time running the Jeep before reversing it, etc.)

I will say that these issues don't seem to exist until after the engine warms up.

I have had 3 separate mechanics look at this and they agree they can feel it but can't get to the source of it without it getting expensive. One guy mentioned the O2 sensors which I will tackle next but I wanted to throw this out there to the community in case anyone has had a similar issue, especially if it relates to REVERSING the Jeep.

Help!

Thanks.
 
It is possible that your IAC is bad. It's not the most common thing to go bad, but it is possible. I'm not entirely sure, but I think that there is a procedure where you can test the IAC (to see if it's bad or not) in the FSM. This would be worth doing.

I'm only going back to the IAC thing, because the issues you describe certainly sound like those of a dirty (or bad) IAC unit.

If you do replace the O2 sensors, I'm going to assume you know only to use OE Mopar replacement sensors?
 
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What are your thoughts on how putting the Jeep in reverse agitates the issue? This is a 6 speed, by the way.

I have had issues like this on other vehicles but I've never seen it get worse for a short period of time after reversing.
 
Jeepaholic said:
Shot in the dark but usually reversing in a manual transmission is a lot more on the gas, off the gas, on the gas off the gas, while modulating the clutch pedal, perhaps this really aggravates the iac? Try driving forward in a similar manner and see what happens
Click to expand...

X2 to this. It still sounds like a dirty throttle body / IAC valve. But like I said, I would test that IAC valve in your vehicle to make sure the unit itself isn't bad. In which case, no amount of cleaning would fix it.
 
Update. So today I dropped the Jeep off at JeepGuys, a local Jeep speciality shop and the joint that did my lift. They wanted to retorque the bolts, etc. since I've put 500 miles on the lift. They also needed to take care of some driveline vibes that are still in there.

Since the Jeep was there anyway, I had them diagnose the rough idle and after a few hours they called me with the following:

1. Plugs aren't gapped properly. Think they're at .43 and they should be at .35 (I think). Had them checked at Firestone a month or so ago after I screwed up the installation (a whole other story) and they said they were gapped correctly. That said, the mechanic looked only at the plug associated with a mis-fire and didn't look at all of them.
2. The TPS is only reading 3.5 volts at the top end and it should be at 5. I honestly have no freaking idea what that means but we shall see if it repairs it. Certainly sounds legit

They're gonna re-gap the plugs and replace the TPS. I am to pick it up tomorrow afternoon.

I seriously hope this fixes the issue bc other than this the Jeep is almost perfect.

Stay tuned...I'll let you guys know if this fixes it.
 
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Make sure they replace the TPS with an OE Mopar unit! Any other brand will likely give you issues.

I hope that fixes it all.
 
Ok. The TPS and the plugs didn't fix the issue.

Finally got the Jeep back after like 1.5 weeks and the problem seems to be pretty much solved. I'm fired up to get the issue gone but what a tale.

I will try to accurately describe what went down from start to finish but I am NOT a mechanic, I didn't take notes and I admittedly kind of stop paying attention to details when a gearhead is rattling off tech specs.

That being said, here is the RATHER LONG run-down based on memory.

The guy at the Jeep shop called me after spending a couple of days diagnosing this and that. He admitted that it was stumping both he and the tech but they had found some minimal damage to gears in the camshaft but weren't convinced it needed repair nor were they convinced that it was causing the rough idle. Something about the aftermarket OPDA chipping the teeth on some gear (thousandths of an inch) in the camshaft. As I mentioned earlier, they also found that the plugs weren't gapped properly and that the throttle position sensor was reading only 3.5 volts when it should have read 5. Whatever, over my head, but they recommended fixing the plugs and replacing the TPS. $279. I said ok.

They did that and weren't satisfied with the results so they called me back. Recommended replacing the camshaft itself. Said the timing was off. They would reset it and it would be in time (right terminology?) but after it ran for a bit it would be back out of time. That's when the rough idle would resume. It was apparently timing correctly mechanically but electronically it kept going out of time. Maybe vise versa. I'm probably way off here but that's what I recall.

They quoted me $900 to replace the camshaft. Painful but I said let's do it because I wanted this damn thing fixed. He told me they would need a few days to do it but would let me know when it's ready.

Then, today I got a VM from him saying he had some "good news" for me....

It turns out that he and the tech didn't feel good about the camshaft solution so they replaced the camshaft position sensor and the problem with the rough idle went away! He believed the plugs and the TPS were contributing factors but the main culprit was the camshaft position sensor. He mentioned something about these sensors being magnetic and if the Jeep sat a lot (it's only got 34,000 miles on it and it's an 06) it can potentially cause them to have problems and/or ruin them.

Anyway, I honestly couldn't believe that he would actually call me up and say they WEREN'T going to do the $900 job!!! He told me he was going to send the camshaft he had ordered back. Honest guy!

Here's the SHOCKER: I was certain I would pay at least $500 or something but he told me that they weren't going to charge me anything for the work they did. He felt badly that it took so long and they had ended up looking at it as a challenge. Also, I'm sure that the fact that I had had them put the lift, tires, bumper on a little while back (not a small amount of money) helped a little here but I still feel this was way generous.

Here's what they did:

Replaced camshaft position sensor
Replaced the TPS with an OEM part
Regapped plugs .40 vs. .33 or whatever they should be
Who knows how many of diagnosing

So...this turned out to have a fantastic ending. Aggravating for sure but still really cool that I was charged nothing when I was expecting an $1100 job to fix the rough idle. Does everything add up? I don't know, but what I do know is that the problem is fixed, at least for now.

Sorry for the novel but I know that I searched high and low for a thorough post about a rough idle gremlin and even when I did find some that were similar to mine, the dude having the problem would never come back and post the result or the solution.

So...here's a potential solution. Camshaft position sensor.
 
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Wow, sounds like you've found yourself a reputable mechanic, those are hard to find! Most of them would never charge you less when they knew they could charge you more, so clearly these guys are honest.

I also know for a FACT that if you are running an aftermarket replacement OPDA (as most of us are), the aftermarket sensors that come on them are notorious for not working properly with our TJs. For that reason, most people buy the aftermarket OPDA, but they replace the CPS sensor on it with the OE Mopar CPS sensor.

I'm actually betting that right there is a huge contributor to the issue. Hell, had I known you had an aftermarket OPDA that would have been the first thing I suggested was replacing the CPS sensor with an OE unit.

Moral of the story here is ALWAYS use OE Mopar sensors on TJs. They simply do not like aftermarket ones.
 
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WPGB1977 said:
Ok. The TPS and the plugs didn't fix the issue.

Finally got the Jeep back after like 1.5 weeks and the problem seems to be pretty much solved. I'm fired up to get the issue gone but what a tale.

I will try to accurately describe what went down from start to finish but I am NOT a mechanic, I didn't take notes and I admittedly kind of stop paying attention to details when a gearhead is rattling off tech specs.

That being said, here is the RATHER LONG run-down based on memory.

The guy at the Jeep shop called me after spending a couple of days diagnosing this and that. He admitted that it was stumping both he and the tech but they had found some minimal damage to gears in the camshaft but weren't convinced it needed repair nor were they convinced that it was causing the rough idle. Something about the aftermarket OPDA chipping the teeth on some gear (thousandths of an inch) in the camshaft. As I mentioned earlier, they also found that the plugs weren't gapped properly and that the throttle position sensor was reading only 3.5 volts when it should have read 5. Whatever, over my head, but they recommended fixing the plugs and replacing the TPS. $279. I said ok.

They did that and weren't satisfied with the results so they called me back. Recommended replacing the camshaft itself. Said the timing was off. They would reset it and it would be in time (right terminology?) but after it ran for a bit it would be back out of time. That's when the rough idle would resume. It was apparently timing correctly mechanically but electronically it kept going out of time. Maybe vise versa. I'm probably way off here but that's what I recall.

They quoted me $900 to replace the camshaft. Painful but I said let's do it because I wanted this damn thing fixed. He told me they would need a few days to do it but would let me know when it's ready.

Then, today I got a VM from him saying he had some "good news" for me....

It turns out that he and the tech didn't feel good about the camshaft solution so they replaced the camshaft position sensor and the problem with the rough idle went away! He believed the plugs and the TPS were contributing factors but the main culprit was the camshaft position sensor. He mentioned something about these sensors being magnetic and if the Jeep sat a lot (it's only got 34,000 miles on it and it's an 06) it can potentially cause them to have problems and/or ruin them.

Anyway, I honestly couldn't believe that he would actually call me up and say they WEREN'T going to do the $900 job!!! He told me he was going to send the camshaft he had ordered back. Honest guy!

Here's the SHOCKER: I was certain I would pay at least $500 or something but he told me that they weren't going to charge me anything for the work they did. He felt badly that it took so long and they had ended up looking at it as a challenge. Also, I'm sure that the fact that I had had them put the lift, tires, bumper on a little while back (not a small amount of money) helped a little here but I still feel this was way generous.

Here's what they did:

Replaced camshaft position sensor
Replaced the TPS with an OEM part
Regapped plugs .40 vs. .33 or whatever they should be
Who knows how many of diagnosing

So...this turned out to have a fantastic ending. Aggravating for sure but still really cool that I was charged nothing when I was expecting an $1100 job to fix the rough idle. Does everything add up? I don't know, but what I do know is that the problem is fixed, at least for now.

Sorry for the novel but I know that I searched high and low for a thorough post about a rough idle gremlin and even when I did find some that were similar to mine, the dude having the problem would never come back and post the result or the solution.

So...here's a potential solution. Camshaft position sensor.
Click to expand...
Such awesome news. Glad you found yourself an honest shop.
 
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Also been having an irritating rough idle issue. Recently put a whole can of carb cleaner through my throttle intake. Just replaced my spark plugs with Autolite Iridiums following Jerry's recommendation. Gapped correctly. Still freaking sitting at 800 or at 300rpms at idle.

Going to replace my CPS with a Mopar unit per your experience. Thank you!


Sent from my iPhone using Tapatalk
 
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Kyle_W said:
Also been having an irritating rough idle issue. Recently put a whole can of carb cleaner through my throttle intake. Just replaced my spark plugs with Autolite Iridiums following Jerry's recommendation. Gapped correctly. Still freaking sitting at 800 or at 300rpms at idle.

Going to replace my CPS with a Mopar unit per your experience. Thank you!


Sent from my iPhone using Tapatalk
Click to expand...

Good luck with it. Pain in the ass. Just aggravating enough to detract from the fun of driving the Jeep.
 
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I already have used ones, Kyle! :lol:

I'm still having slight idle problems too and I'm just going to replace everything!!

I go on Amazon and the selection of wire is, shall we say limited?
 
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tman66 said:
Can anybody recommend plug wires for a 2002 4.0?
Click to expand...
factory.... any wire can fail over 20 years... if you want aftermarket, the list is limitless.... who is yer best parts guy? I go to NAPA cuz everyone else is over an hour away.

I just bought a Husqvarna snow blower because the dealer is 1 block away. And if it ever needs tuning, I can "drive" it to him.

I grew up when Isky Cams were the only choice for drag racer wanna bees.... Not cuz they ground a better cam but because they marketed the shit out of their "triple" grind.... and they gave every Tom, Dick and Harry contingency money to put their sticker on their fender. Their cams were a quality product sure but only equal to all the other quality choices out there. So after market plug wires? In a DD TJ? They are all equal, unless they are half price. BUT $$$$ will not likely get you a better plug wire. shop local, be happy.
 
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