Honda: idling, air control valve, accord lx

Question
When I am stopped my car idling drops to half an rpm when in drive. I can put it in neutral and the idle isn't as rough sometimes. When starting the vehicle I have no problems but as soon as I let it sit there it will drop. My dad thinks it might be something like an "idle sensor" but he doesn't know exactly. My car is a 93 Accord LX.

Answer
Your dad is on the right track,sound like you  need to clean the idle air control valve just get some throttle body cleaner at the auto parts and follow the directions.You may also need a tuneup.By the way the 1 on your tachometer  is for 1000 so half way to one is 500 rpm.