Cleaned the IAC valve, ran great, now back to sputtering and dying

johny_knoxville

johny_knoxville

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Dec 28, 2020
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Amelia, Ohio
Per the excellent documentation, photos and great advice on this forum I was able to (halfway) clean the IAC valve and ole Fern was back up and running, for a week. Same problem came back like gangbusters. So I purchased a new IAC valve and installed, still having issues. Could NOT cleaning the housing that this connects to get this result?
The way you have to keep your foot on the gas even at 35mph makes me think fuel pump, which me and my buddy are willing to do. Just looking for advice, 2000 Wrangler TJ Sport 4.0 156K auto. Battery, starter and TPS have been replaced.
I realize how many threads and posts there are for this and have read them, just trying to get guidance from experienced folks. Thanks in advance!
 
Did you remove the IAC to clean it or did you run cleaner through the TB at idle rpms as I consistently recommend here? Running the cleaner through the IAC at idle rpms cleans not only the IAC but also the orifice inside the TB that the IAC's plunger fits into. A dirty orifice can cause the same problems a dirty IAC does.

Also, does this sputtering problem affect the engine equally when it's cold vs. warmed up? If it only happens once the engine has warmed up the problem is more likely caused by a defective upstream O2 sensor.
 
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Thank you for the advice. I removed it to clean it initially. Its difficult to get it warmed up as it won't stay running long enough but after last night I would say equally. It ran great initially after cleaning the IAC valve, but now its back. I will get the orifice clean hopefully tomorrow and update. Thank you again for the information!
 
@MrMark52 I had access to a code reader, but, of course it was NOT throwing any codes. Here is an update:

- New Battery
- New Starter
- IAC Valve (new one installed and throttle body cleaned while installed)
- New Autolite XP985 Plugs (previous ones were way over gapped and black)
- Grounding strap from hood to body, and body to engine was frayed and worn, both replaced
- Left battery unplugged overnight to "reset" computer

The weird thing after every replacement/repair, it runs great then just chokes/bogs down like not getting fuel. I plan on replacing the O2 sensors ( I realize they normally throw a code) but am doing easiest and cheapest working my way back to fuel pump. I figure its a 20 year old Jeep with 156k, couldn't hurt to replace this stuff anyway. :) Thanks again for everyones help and advice, still plugging away at it. (Chose that as my profile pic since thats usually how I see ole Fern as of late.)
 
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When you have access to a Scan Tool (Code Reader) check the Upstream O2 sensors voltage readings; generally .9V is Rich and .1V is Lean. The normal voltages when warmed up should be .4 -.7V
When the engine is started Cold the fuel trim is regulated by the default programming in the ECU; this is called Open Loop.
When the engine is warmed up, the O2 sensors are heated, the ECU will control the fuel trim by O2 sensor voltage readings; this is called Closed Loop.
Sounds as though the engine runs good while Cold in Open Loop, but once it shifts to Closed Loop that is where the problem lies.
I agree with Jerry.... check the voltages for the Upstream O2 sensors and see what the voltage readings are in Closed Loop operation.
 
CharlesHS said:
When you have access to a Scan Tool (Code Reader) check the Upstream O2 sensors voltage readings; generally .9V is Rich and .1V is Lean. The normal voltages when warmed up should be .4 -.7V
When the engine is started Cold the fuel trim is regulated by the default programming in the ECU; this is called Open Loop.
When the engine is warmed up, the O2 sensors are heated, the ECU will control the fuel trim by O2 sensor voltage readings; this is called Closed Loop.
Sounds as though the engine runs good while Cold in Open Loop, but once it shifts to Closed Loop that is where the problem lies.
I agree with Jerry.... check the voltages for the Upstream O2 sensors and see what the voltage readings are in Closed Loop operation.
Click to expand...
Thank you sir I just downloaded something called torque that I can run on a laptop with my usb obd reader. I’ll get on it today when it warms up! Much appreciated!
 
As mentioned in the original thread you were posting in, you don’t need a code reader to get codes - do a “Key On/Key Off” sequence three times, the third time leaving the key on - any codes will show in your odometer.
The Torque app is equally as good if not better for reading codes.

But if your not getting codes, I’m thinking water in gas or (as you’ve mentioned before) failing fuel pump.

Water in gas will not throw any codes that I’m aware of.
And I don’t think a failing fuel pump or fuel pressure regulator will either. Both are replaced together as an assembly when you get a complete fuel pump. But you can borrow a fuel pressure tester from one of the auto stores to test fuel rail pressure

FWIW - (and I don’t remember all the exact details) When my fuel pump was failing the Jeep was just getting harder and harder to start. I borrowed a tester from O’Reilly’s and pressure tested within spec which only proved the pressure regulator was good. The key to my diagnosing it was the fuel pump is/was that if I turned the key to on and listened for the pump to run, sometimes I could and other times I couldn’t hear it run.
And I know water in the gas is unusual these days, but it does happen, even though the alcohol in the gas can absorb some very small amount of the water.

Bottom line - need to figure out if your issue is fuel related or electronics related.
 
Good morning sir! Thank you for that, but now the plot thickens. When I started it up for the first time yesterday, she started no problem and ran ALL DAY 0 ISSUES!?!?! WTF? So for now, I am waiting to see when/if it dies next. Someone else mentioned water in the gas and recommended running Seafoam through it? I have a bottle of Lucas fuel system cleaner I was going to try when the gas gets lower. Thanks again everyone for all of the input.
I CAN hear the pump kick on when I first turn the key. Totally agree with last statement, before I replaced the grounding wires I could jiggle them and the car would die. I wonder if ole Fern just needed to adjust to all the awesome new stuff and said, "I can work with this, for a while" lol. :)
 
When things like fuel pumps and fuel regulators, some sensors, and various other things are going bad, it’s not necessarily a black/white failure. Component failure can be intermittent, or fail at once altogether.

Once again, codes will hopefully give us some clues. And just because you don’t have a CEL doesn’t mean there aren’t any codes.

The SeaFoam is a great idea. It’s good stuff.
But it’s use will likely only help in finding the problem, not fixing the problem.
 
Thank you everyone for your input and suggestions. I ended up taking it to friend of mine (mechanic) and he replaced the Crank Position Sensor and the faulty Oil Pressure Switch. No more oil leak and she runs great now! :)
 
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