Most of the time it idles around 800rpm when I’m at a stoplight, in gear, with brake on. About 50% of the time it will idle down afer 20-30seconds to about 500 rpms which causes alot of vibration and it sounds like the engine is running very rough. I recently changed the spark plugs to see if that would help.
Any ideas?
The computer controls idle speed via the Idle Air Control (IAC) valve. If the valve is dirty or sticking it can cause inconsistent idle speed. Clean the IAC valve and see if that helps.