engine surge

[droptine]

i have a 99 ranger 4.0 with the defroster on the engine wants to surge. while in gear at stop light truck will lunge forward. even while driving down the road can feel surge each time compressor cycles. any ideas?

 

[snake]

The PCM is programmed to take the idle up just a bit when the compressor kicks in to compensate for the additional load on the engine. I'm not sure if it is controlled by the IAC or not- but whatever controls it is on steriods it sounds like- overcompensating and raising the idle up too much. Just a theory.