My car runs great. It is a 99 C70 convertible with 230,000 miles.

Problem is that at idle, it revs to about 2k rpm, then drops down to 900 or so, then back up to 2K, back below 1k over and over.

I am thinking maybe an air valve?

The machine runs great at any RPM above 2k, and even lower when under load, like if I am in traffic. It just will not idle well.

Any ideas?

 

Possible bad mass air flow meter, you can order this part online and replace it yourself

 

Unplug the MAF and see if you get a CEL. Also, the car should run better. That's usually indication of a bad MAF.

Other area to check is the idle air control valve being gummed up. Clean it up with some brake cleaner.

 

Unplug the MAF and see if you get a CEL. Also, the car should run better. That's usually indication of a bad MAF.

Other area to check is the idle air control valve being gummed up. Clean it up with some brake cleaner.

 

You can also try cleaning the MAF sensor. Buy some CFC Mass Airflow Sensor cleaner... see what happens before your buy a new sensor. Most auto parts store should have it - even some Home Depots... Check Youtube for FCP's vid on how to remove the MAF.