ryanm

I took my 2000 cherokee in for an oil change, and they also checked the air filter (K&N), other than that, just fluids were checked.

It may or may not be related to the above mentioned service. But, sometimes when the truck sits at idle, the idle fluctuates up and down about 100 rpm. it goes up for 3-4 seconds, then down for 3-4 seconds, and back and forth.
Throttle from there is normal.

Where should I go looking?

Thanks

PS. I'm pretty new to cherokees and jeeps in general, so go easy on me.
I come from the world of a 1987 BMW e30 (325i)

cpnwrench

Hmmmmmmm.....was the idle fluctuating prior to bringing to shop for oil change?

did you check their work to be sure they secured any and all vacuum lines related to the filter work? liek to filter area/map sensor/intake manifold pipe ports etc etc etc?

and where, pray tell did you bring your Jeep for this service?
if you say jiffy-lube.....I m gonna .

cpnwrench

cpnwrench

BTW.....I also have a BMW 1992 525i.....Just awesome on highway. (better than a Caddy or Lincoln for ride and quiet.)

Jeep Cherokee 1991.....Just awesome NOT on highway!
(better than anything I have ever had in snow/mud/sand/dump)

cpnwrench

Bustedback

Is the A/C or defroster on when this happens?

ryanm

sometimes i think it happens when i turn on the defroster.

but it was also doing it when i turn the air all off.
ill double check. but its not doing it all the time.

could it really be due to a coolant level?

andyg

Sounds like the IAC might be sticking or the computer is getting false info thinking it needs to open it. You could unplug the iac for a bit and see if the idle stabilizes, but it will affect the idle with the a/c on.

Bustedback

The PCM kicks the idle up when the A/C compressor kicks on to compensate for the load of the compressor. It also does this when the electric cooling fan comes on to make up for the extra load from the alternator.