Toyota Repair: Rough idle only in gear

Question
Hi Ted,

I have a 97 Celica with 180k on it. I am the original owner. The car runs smooth while in park or neutral but vibrates while in Drive. I only notice it while stopped. The motor mounts were replaced last year when it failed inspection so I don't believe that's the issue. I notice that it idles in drive around 600 Rpm and goes up to about 750 in park or neutral. Could the idle just need adjustment or is that just cheating it and hidden a problem?

Thank you,

Anthony

Answer
The idle is not adjustable on this engine it is controlled by the idle air control valve if the idle is too low it can cause a vibration, it should be around 800 rpm, if the vibration is there at that rpm it should be checked for any contact between the engine, transmission and exhaust system and the body. If the idle is too low, around 500 or less the idle air control valve may need to be replaced. The idle of 600 rpm is a little on the low side, if the vibration stops by applying throttle to 750 rpm in gear the problem is the IAC valve.