New idle control valve correct part?

[dlpalumbo]

My '90 C4 has always (for the 3.5 years I've owned it) suffered from an idle bounce. That is, when I lift the throttle with clutch disengaged, the idle will fall below the 850 RPM point then bounce back up. Its as if the ECU doesn't have a good guess at what the idle valve opening should be. Sometimes it will even stall. I've gone the usual route in addressing this issue and decided, at last to replace the valve.

As you may know, the valve is $320 through Pelican. I found some folks offering $260 and one offering the valve at $150. I decided to try the $150 part as it looked identical in pictures and I figured I'd compare the one on the car with the replacement to make sure it matched before I put it in.

Well, the replacement had the same Bosch part number so I installed it. As I was expecting, there was very little change in the idle behavior. However I became suspicious that the valve might have been replaced by the PO with the cheaper unit so I decided to see if I could read the part number of the more expensive parts from their web pages.

The part numbers matched except for the last 3 digits. My ICVs end in 514. Pelican's and others in the $300 price range end in 531.

Has anyone replaced their ICV (ISV) with an aftermarket unit of a different part number and had a similar idle issue??

Cheers,

Dan