In the last 2 days, my car has check engine light and the car runs like it's misfiring when the a/c is on. I recently changed the spark plugs and accessory and serpentine belts. I'm wondering if anyone else experienced the same issue. I'm going to get ad ODB reader and see what the codes. It's strange that when I have the a/c off, the engine returns to normal. Any help is greatly appreciated.
Thanks for everyone's reply. The code stored and pending is P300. I've used factory plugs and the a/c belt tension is within specs.

 

hmmm... what kinda plugs did you use ? and were they gapped to spec *most come pre-gapped but some don't*


2nd question is everything torq'd down to spec ??? .....

 

Hmmm...get the obd 2 and let us know.

 

My guess is that when you turn the AC on and the compressor is running something is causing a drag... maybe you didn't install the belt correctly? Something too tight. That's the only thing that makes sense. Maybe its not misfiring but there is extra drag on the engine at idle when its trying to spin the AC compressor