I have a 97 Acura CL and at idle and "D"(rive) the tach reads 750 or so. When the AC compressor kicks on the idle drops to about 600 and there's is a irritating vibration. I've read in the helm manual (for my 97 prelude) and noticed that the ecu is supposed to get a signal from the ac and boost fuel/air or something to keep the idle at 750!? Is this true, or does the idle supposed to drop?

If i hold the brake and raise the idle to 750 or higher the vibration goes away.

What do you guys think needs fixing?

1) ac not sending signal to ecu
2) engine mount
3) balance belt
4) compression
5) iac valve
6) other

I know as a last resort would be to raise the idle but rather fix the problem no mask it.

Thanks in advane...

Jay