Hey guys I've been running into a problem lately where if I am stopped at a red light and the windshield heater is on... the RPMs will surge up over 1k and go back down then a few seconds surge back up and go back down. If I don't have the heat on it's fine. When I am driving and the heater is on I don't really notice it as much. The RPMs actually surge so much that I have to really plant my foot on the brake so that the car doesn't move.

I'm wonder if this could be a vacuum line or something? Which would be great and would probably fix another problem I having.

 

Defrost also runs the A/c compressor. It's probably surging from lo refrigerant pressure. See if it does the same when in A/C.

 

Thanks for the reply, that makes sense because I recently lost most of my cold air when the A/C is on. I will check it next time I go for a ride.