Flucuating Idle!

[Lowrange2]

It just started doing this stuff today! I hate car problems!
Anyways, I noticed that while sitting in a parking lot at the post office that my girlfriends 1999 Grand Cherokee 4.0L was idling way high. When I start the jeep, it idles around 2000 RPM for about 10 seconds then flucuates back a forth between 750rmp to almost 1500 rmp. For example it will stay around 750 for a few seconds then jump up to 1500 for a few seconds and go back down and repeat, Constantly until i put it in drive! While driving the rpm still slightly flucuates noticably. I have no idea where to begin. All of this is happening when the A/C is off, so its not the compressor kicking in. It's damn annoying! I hope somone has had this problem before! Help! please! Andyhasta

 

[Speed_racer]

Andy.... buddy... you have no car.. by any means...

 

[Lowrange2]

my bad! I hate automotive problems!

 

[Lowrange2]

No one knows then huh?

 

[Speed_racer]

Patience, grasshopper.

Probably thrown off by the "car" question

lol, jk.

How new is your 02 sensor?

I would definitely say this is a sensor issue.

And, btw, learn to love your Jeeps, and their issues!

 

[casm]

No one knows then huh?

1999 Grand Cherokee 4.0L

Ask over at NAGCA, or in the Other Tech forum. This is not the same vehicle as an XJ or MJ and has its own set of peculiarities to go with.

 

[Lowrange2]

Aight will check those... How many o2 sensors are in on this thing... please pardon for the comment in the wrong forum! I own an XJ myself and did'nt think anything about putting it in a different forum...

 

[JTwthaXJ]

Run the RPMs up to about 3K and cut it off, oh yeah and cut anything that uses the a/c compressor off. This will cause the idle air control valve to completely close. Crank it up again and see if it idles any better..... If not possibly the idle air control valve or maybe the MAP sensor, both of which can cause a rough idle (both should trip the check engine light though and are located on the throttle body.) As long as it has the 4.0L there should only be 2 O2 sensors, one on the collector pipe and one on the catalytic converter. You can occassionally pull these out and run a wire brush over them and that will clean them up. As for the other two sensors if they are bad you have to replace them, no quick fixes.

 

[xraydivr]

theres an o2 sensor on the exhaust under the "car" that the connector gets dirty or the wire sometimes melts