Surging Idle

[col320ce]

I have a 320CE w124.052 M104 engine
The car suddenly started idle surging. It is only at idle; if I put my foot on the accelerator even just a tiny bit (not enough to increase the revs) is completely goes away. Lights go dim then bright when it is surging. Its worse after I come to a stop.
The wiring harness has been replaced as has the wiring to the throttle body. Cruse control works.
I've checked for vacuum leaks, tried a good MAF and OVR. It sounds to me like a stuck idle sensor/governor switch or something. Any suggestions on what it is and which bit I test next?
Thanks for any help...

 

[mioba]

Had this moons ago with my w124. it was a vacuum leak of i recall

 

[col320ce]

I've pulled the purge valve out and I can blow through it in both directions and putting 12v across it does not seem to do anything. I think this could be the culprit... I'll replace it and see what happens.

 

[col320ce]

It was the purge valve. Back to a beautiful idle again.