Rep Power: 0

Good day! I have a Civic LX 2001, 117K. Until yesterday when I started the engine it had about 1000 rpm, then it dropped to 700-750 rpm. Now it starts at 1000 rpm and goes lower to 600-650 rpm. The car vibrates a lot. When I shift from P to R it stops vibrating for a second and then vibrating gradually increases, same for P to N, and N to D (and has no change between D to D3 or 2). I do not notice any changes in acceleration or power at high speed , however, the engine does not sound quite right. The actual vibration is only noticeable when I stop at a stoplight. It is not engine mounts, I've just changed them. Please help!

 
Rep Power: 811

sounds like you may need to clean the intake system. in particular, the iac valve on the throttle body. its the piece where the two coolant hoses go into. remove that and spray inside with carb cleaner to get out any black carbon and junk.

 
Rep Power: 0

Thanks, that helped.