Hi my name is michael. i bought a 2001 cherokee xj sport. it has A.C.
My problem seems to be that it idles around 600rpm and when i put the heater motor on (heat or A.C.) my idle starts to jump up about 200RPM. would be fine if stayed there but it kicks up and down about every ten seconds. is this low high idle normal under electrical load? the battery was weak when i bought it, so i replaced it with a red top optima. my voltage meter stays constant while running, doesn't change with RPM so i don't think its the alternator or is that a false assumption? Any help would be greatly appreciated.
Thanks

 

The symptom could be nothing more than a dirty IAC (idle air controller) plunger which is used to meter air into the throttle body when the engine is idling. Its usual symptom is an unusually high RPM or very rough/low idle. It can stick if dirty when first accelerating causing a stumble. It is removed just like the TPS, it's at the 12 o'clock position if you orient yourself so the TPS is at the 3 o'clock position. Remove it and use an aerosol throttle body or carb cleaner together with a small brush like a toothbrush plus cloth to gently clean the IAC's solenoid-actuated plunger. Don't screw with that plunger, just clean it gently. Also thoroughly clean the hole the plunger fits into. Might as well clean the interior of the TB and backside of the TB butterfly valve while you're in there.

If that doesn't take care of the issue, replace the throttle position sensor that is also mounted on the throttle body. The TPS is sealed so it can't be cleaned. The TPS is what tells the computer how much throttle you're giving the engine via the accelerator pedal.

 

thank you very much, i am going to do this tomorrow and just for safe measure i am going to swap out the spark plugs and air filter at the same time.