Jeep Grand Cherokee has fast idle cold then stalls when warm.

[jeepjerk]

1993 Jeep grand cherokee with 4.0L EFI straight 6.
I have done a recent tuneup and replaced the IAC motor and a new O2 sensor.
Still need to check map sensor and probably temp or crank sensors.


I know there are probably a million threads just like this.

I think I have gone through about 4 IAC motors and 3 oxygen sensors in this jeeps lifetime fighting this idle problem.

But this seems different in a way. At a cold start the idle will go way up (2K)
Sometimes engaging the AC will bring it down.
Then after it warms up the idle goes really low (500) and the engine wants to stall when put into drive.
Now what is really strange is that when idling low it will go into reverse and not threaten to stall???

Now I just replaced the IAC motor and it adjusted the idle fine after a computer reset (pull neg bat terminal).
Now back to high idle cold and warm stalling in drive.

I read the codes and found oxygen sensor fail code. So changed the o2 sensor and reset.

Still the above symptoms.

At this point I am at a loss.

Thanks for any help.

[Saudade]

I'd suggest you ask this in the *Grand Cherokee* forum. This is the XJ Cherokee forum. Not that we're unwilling to help, but the XJ is different enough. The other forums will likely be much better help to you.

And welcome to AF.

[jeepjerk]

Well I'm sorry. From what I can see I'm in the Cherokee forum.
Can you get an admin to move this to the proper forum for me?
thanks

[Saudade]

The GC forum is here.

http://www.automotiveforums.com/vbul...splay.php?f=29

I would just copy/paste it rather than wait for an admin.

Good luck!

[fredjacksonsan]

Originally Posted by Saudade

I'd suggest you ask this in the *Grand Cherokee* forum. This is the XJ Cherokee forum. Not that we're unwilling to help, but the XJ is different enough. The other forums will likely be much better help to you.

And welcome to AF.

Saudade, you are correct - unless jeepjerk has the 4.0 engine, in which case this might be the better, though incorrect, forum since there's a lot more traffic, and the engines are identical enough.



jeepjerk, what year is your Jeep and do you have the 4.0?

[I've seen the other thread in the GC section. If it's a 4 liter and anyone here has a thought, I'll leave this thread open.]

[jeepjerk]

Yes this is a 93 with 4.0L EFI straight 6.

Starts with idle way up. As it warms up idle goes below normal and wants to stall out in drive.

When put into reverse the stalling problem isn't there???

Do you think this is a trany problem or engine problem or both??

[jeepjerk]

I've replaced the wires and cap within the last year. I checked the cap and it looks fine.

There is something here that I'm missing.

I started the car this morning and the rpm was about 1500 and was slowly creeping up to 2000.
I put it in reverse to back out of the garage and it worked fine.

Then put it in drive and from 2000 it was pulled down to about 300 and seemed like it was going to stall.

Is there actually a pvc valve in these cars? All I see is a hose going from valve cover to filter box.

[jeepjerk]

Today I checked the MAP, MAT, and ECT sensors. whew

Everything tests good here.

When I pull the vac line off the MAP sensor my high idle goes to normal but according to the voltages it's working correctly.

I checked every vac line for leaks and found none.