96 Saturn SW2, 85000, 5-speed. I thought it was running bad when the engine warmed up, but it appears to be greatly affected when the a/c gets turned on. In the past few weeks I have had a temperature sensor and an O2 sensor replaced. I understand that running the a/c saps power from the engine and thus performance will be degraded. When I run the a/c my car runs more roughly. It has many small hesitations, like a shaking almost. When I turn the a/c off, it smooths back out. I’m about 99% convinced the a/c is causing something, but perhaps it is merely amplifying an existing problem? I’ll be taking it to the service station after I get paid, but I wanted some opinions first.
When the a/c is on, a signal is sent to your engine to make it run faster. Maybe whatever is supposed to send the signal is not working, and your engine is stumbling when the a/c kicks in. Check your fast idle relay or fast idle solenoid.
Patient: “Doctor, it hurts when I do this!”
Sorry, I had to say it.
I agree with Hyperelastic. When the AC is turned on, the RPMS are bumped up a bit so the engine doesn’t die when the AC robs power from the engine. With carbed cars, and solenoid pushed the throttle a bit to increase RPM, with computer controlled cars, it can be anything from a solenoid to adding fuel and/or modifying spark tables to achieve this.
Thanks for the input. Sounds reasonable to me. You watch though, I get paid next week, we’ll have a cold flash and I won’t turn the a/c on for a month!
I had the same problem. It was a vacuum leak. The mechanic replaced a short, cheap piece of hose and the problem was solved. Sometimes it’s that simple.