90 dies when up to temp

I searched and found similar problem but none that matched my identical issue. Ive also tried some fo the suggestions in those threads with no luck

90 4.0 L auto





Ive been fighting this issue for over a year, here is the story so far.



Jeep developed a rough idle when warm, then eventualy it started dying when you would let off the gas while driving, and when comming to complete stops. I learned to keep it running by putting it in N and holding the throttle at approx 1200 rpms until stopped. If it dies and you restart it it idles fine, but it will not idle if you give it gas and then let off.





I thought TPS. I replaced it, and it cured nothing. I unplugged the TPS and the problem went away. But with the TPS unhooked it idles rough when cold and has a dead spot in it.



I figured that meant the new TPs was bad. So I replaced it with a differant brand. Problem stayed the same, again I unhooked the TPs and it runs fine once warm now.



I have messed with the EGR, I unplugged the vaccum hose while at idle and no changes there and I can watch it move in and out when I rev the engine.



I removed the IAC and it moves in and out when you turn the key on, I started ti without the iac in and it moved out to try to compensate for the air flow.



I left the IAC unplugged with TPs plugged in and the issue stayed the same with no other effects.



Did the same with the EGR valve.



I've tried TPs plugged in with both the IAC and EGR un plugged, problem is still there.







What am I missing?

have you checked for good spark? mine used to die when warm and it was due to a failing coil. mine would start fine when cold but once it got warm it would want to sputter and die at low RPM. when it died it would usually start after a few minutes after it cooled a little. it also would miss under load, might want to have it tested.

If it was a spark issue why would it run witht he TPS unhooked without issue?

is the TPS properly adjusted?

Yes it is within range.

I'd start with a thorough cleaning of both the throttle body and the idle air control. I've seen this create the symptoms you are describing.... Here is more.
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The Idle Air Control (IAC) is mounted on the back of the throttle body. The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality

I have "profesionally" cleaned it at the shop I work at, and Ive also cleaned it while swapping the aprts around, Forgot to mention in my post.

Just because the EGR valve is unplugged, that doesn't mean it isn't leaking exhaust gasses into your intake due to the fact it isn't seating properly.

Have you ever checked for other vacuum leaks?

For instance where the intake manifold meets the head. I always recommend that folks snug up all their intake manifold fasteners with the engine cold just for good measure. They're very prone to loosening up.

Check fuel pressure.

crimsondragon said:

Check fuel pressure.

Click to expand...

Always a good idea.

Test the O2 sensor, and the MAP, CTS and MAT sensors while you are at it. Any one or combination can be part of the problem.

http://www.naxja.org/forum/showthread.php?t=1012701

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Also what about (consider), Cap, rotor, spark plugs, distributor wear, and possible manifold or vacuum hose leaks.