why does my rpm drop when my car is idling at a stop and the heater or a/c is on?
when I'm stopped at a red light or stop sign and my heater or a/c is on my cobalt acts like
it wants to stall out. My engine temperature fluctuates between 189 to 196 degrees.
a couple things.. so if your heater/AC is NOT on it idles fine at stop? Is heat on defrost? Could it be the AC compressor kicking on? Maybe check fuel pressure. Possible tune up
Dirty or faulty idle air control valve. Clean or replace it as needed.