Chaps

I have recently aquired a 1994 C280 I6 M104.

It has a problem:

Car starts fine, idles fine when cold.

When engine starts to warm it goes lumpy, rough and if driven surges.
It will rev freely and once above about 1000rpm is sweet but when accelerator pedal is released the revs drop and sometimes stall and sometimes runs lumpy again.

Once the engine is warm it is beautiful, smooth, idles and revs freely.

Its only rough when warming up.

OVP is new type, bypass relay does work but I am curious to find out when it should kick in.

What are the sequence of events when the engine is cold to when it is warm, what switches in and out?

What other things could I try, Coils etc. can be ruled out as once warm it purs like a pussy cat.

Si.