1990 190E 2.6 surging at idle
 

Have a 1990 190E 2.6 At cold start it idles high. At operating temp at idle it surges from 1000 to 1500 rpm in neutral and park. It idles high in drive but does not surge. It does not surge with the air conditioner on but still idles high. I can slow idle to correct value and stop surging by clamping the idle air hose. I have the service manual on CD, it shows a 25 pin connector on the CSI control box and this car has a 35 pin connector with not all slots used. Thus I am handicapped in the trouble shooting arena. Wiring diagram is different and wire color codes are different than what is on the car. I suspect overvoltage protection relay or idle air valve but with different wiring than is shown in the manual I can’t trouble shoot by the book. Idle air valve is not getting 12 volts. When hot wired I can detect a slight click but not what I would have expected and cannot see any detectable movement when looking into the valve when hot wiring it. The fact that the ac running makes the surging stop makes me wonder about the idle speed controller. Anyone having words of wisdom to share or suggestions would be greatly appreciated.

Is the TVS working properly? If it doesn't send the idle signal there is no idle speed control. Unless you also have a ABS light on the dash the OVP relay is probably okay.

Duke

Idle
 

Sounds Like An Air Leak.

Not to find fault with Duke's post, but OVPs can be bad and not produce an ABS light. Been there.

Pull the OVP and simply shake it. Be sure to hold the flap that covers the fuse(s) down. If you hear any rattling, something's come loose inside and the device needs to be replaced.

Also consider Duke's TVS discussion and Stevebfl's comments in the following thread:

http://www.peachparts.com/shopforum/showthread.php?t=37410&highlight=ovp+rattle