wierd idle

2000 jeep cherokee. When the car is warmed up and when the heater is on, and only when the heater is on, the idle will increase really quick, and then go back to normal. This usually happens every 5 minutes while at a light or when stopped. :rofl:

Maybe your air compressor is kicking on. Try it at home and see if the idle co-incides with the clutch on the compressor engaging. You will know it when the compressor turns with the belts.