Why is my car idling so rough? I recently had my rear O2 sensor and the wires replaced. This fixed the problem I was having with the engine and check engine light that had been on. Now my car idles very rough at around 700 rpms. It used to idle a bit rough once at Normal Operating Temperature. Now its every time that I'm idling. It hasn't stalled or seem to come close to stalling, but I'm concerned that this may lead to another problem over time.

What should I check first? I read some forums and I kept seeing "check the IAC valve", but I don't to look for, or what to get to clean it. I know where my IAC is though. I had bought the car from a friend and don't know everything that has been done to it. I'm going to get an oil change this weekend, hopefully that will help. It couldn't hurt as I see it.