My 93 Honda accord has recently started abruptly dropping the RPMs from 1500 to 1000 then immediately back up to 1500. This occurs after I have been driving it a while and only occurs when idling. The engine doesn’t die, but it is annoying. Any idea what could be causing this and is it causing damage to the engine? Thanks in advance.
Engine idle is controlled by the IAC (Idle Air Control) valve. You may need a new one. Another possibility is a disconnected or leaking vacuum hose.