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?

 

when was the last time you did a tune up?

I would also do a comprestion test..

 

Check condition/test voltage at all coolant temperature sensors.

 

Failing to see what plugs and wires have to do with the issue if it runs FINE without the TPS hooked up? But plugs where changed sometime last year, wires have never been done. I took the original plugs out at 168000 miles. Its at 174000 now.

 

I ment to say check the plugs not do a tune up my mistake.. I had a carbon build up that cause a similar problem turned out out part of the piston denated from bad gas... thats why I said to do a compression test.. sorry about that...

 

The other thing that might help give this a read
http://www.lunghd.com/Tech_Articles/...iagnostics.htm

 

No worries, Im just trying to understand whats being said.

I changed the plugs when it first developed the rough idle ( forgot to mention that)
Number one plug was a bit rough looking but Ive since pulled the newo ne and nothing visably out of the ordinary.

I asked this quesion on numerous jeep sites and not a single person has suggested the same thing as another person. Sounds like I may just need to get an entire intake from a JY motor and swap it just to see what happens. If nothing happens im out $20 for the intake, a few for the gasket and some time.

 

What is the voltage read out on your current tps?
and you did you read the Link i sent you?