Hi,

A friend of mine has a 1998 Jeep Grand Cherokee Laredo 4.0 automatic with 135,xxx miles on it. with a weird problem..


Problem - It will start up fine and then start stuttering (RPMS will rise and then go down to near 100) in the first five minutes. It seems to resolve on it's own. It will also do this within the first five minutes of driving at any speed.


Solutions - We've replaced:

- Crankshaft Sensor
- Throttle Position Sensor
- Plugs/Wires/Rotor and Cap
- Cleaned the carbon deposits from the throttle body
- Had fuel pressure tested came back normal
- Coolant Temp Sensor


Outcome - Still seems to stutter intermittently in the first five minutes of idle or driving.

Can someone HELP??!!

Thanks


*******Update - We have found the problem! It was the upstream 02 sensor. Replaced it and the stutter has completely gone away.

 

Could it be the IAC?

 

Is the defrost or A/C on while this happens?

 

most of the time yes.

 

There is the problem. The idle will increase any time the A/C compressor kicks on.

 

I thiiiiink you misread.

 

The RPMs go down to 100RPM?

 

I have a similar issue with my XJ, it doesn't quite drop that low though. Clears right up within a few minutes. I'm real curious to see where this goes.

 

The RPMs seem to go anywhere from 100-200 rpm to 1500ish rpm without ever stalling out.. It's been doing this for about a month now.

 

Check the plastic line that goes to the MAP sensor for cracks.

 

Ok today we cleaned the IAC and looked at the map hose for cracks, no cracks.

Neither of these fixed the problem.

It actually stalled today for the first time as well.

We have a checklist of things we are checking but nothing seems to fix it.

Does anyone have anymore advice/info about this?

 

There is an o-ring under the mounting of the IAC. It may be dried out, cracked or hard. Try replacing it.

 

Did it stall while driving or when coming to a stop with your foot off of the gas?

 

When it was stopped with foot off the gas.

 

But it runs fine if your foot is on the gas? Replace the IAC motor.