Strange idle: 2.6L 5-Sp 190E

My 190E has had some problems starting. Cold-it starts easily. Warm-difficult with one or two cylinders catching after some time then it finally has all six firing. I figured a fuel pressure problem and I was all ready to pull the checkvalves when a new problem started today. Once the engine warms up, the idle surges between 1400 and 1800 RPM. It will surge four or five times and then settle down to about 600 RPM (which seems low to me). Plugs, wires and distributor cap are new. K&N filter in good shape(nothing obstructing). The checkvalves may be the problem for the hard starting, but the idle surge has me baffled. Any ideas? Thank you and Happy Holidays to all.

[mplafleur]

Mine did that tody for the first time EVER. Only once, after the engine was warm and I just restarted it. It was surging between 1000-1500 RPM (I think) and would not idle below 1000. I did not have patience with it and let only occur a few times. I put the car in gear and drove off. The darn thing actually stalled out once!!

The symptoms have not returned since then. I'm not sure what it could be, I hust rebuilt the engine and got it on the raod two weeks ago. It had been running better that it ever had.