89 300sel surges at idle, intermittent... I've read, and read.. Help please??

[jay3000]

Engine runs well otherwise, but on some occasions, it will have a rythmic surge at idle, especially when in gear. Sometimes it runs beautifully, and idles smooth as silk.

All tune up parts are relatively new, and even has a new O2 sensor. I removed, and cleaned the idle control valve with throttle body cleaner. It wasn't very dirty, and seemed to have no effect.. The OVP relay is apparently the old style with one fuse, but the ABS light has never come on, which leads me to believe it's OK..

This seems to be a common problem, as there are plenty of posts about it, but I can't seen to find any posts where someone has found a successful cure..

Anyone know where I need to start looking???

THanks,
Jay