Rough Idle with Heat on

[Jadenjdawg]

Hello all. Hoping this is an easy solution. My truck has recently started a horrible Idle problem. When the Heat is on, the truck will IDLE between 500 and 1200 RPM's. And, it is a rapid jump. It will bog down to 500 and almost kill the engine and all of a sudden jump up to 1200. If you do not have your foot on the brake, it will jump enough to scare you. It seems the compressor is kicking on and causing problems. When the heat is turned off, the truck purrs like a kitten at round 700 RPM's. 1998 4.0, Automatic with 90,000.

 

[kimcrwbr1]

My first thought was the A/C compressor may be going bad disconnect the compressor and see what happens. My jeep cherokee would cycle the A/C in defrost to remove moisture from the cab maybe the idle air control is just trying to compensate for the low idle when the compressor is on.

 

[LIMA BEAN]

Yea it kicks on in like defrost and floor as a drier for air. Unplug it and see what happens.