Having just replaced the head gasket on my M102 engine and put it all back together, I now have this problem which I've been trying to work out for a week or two.

1. The car starts instantly from cold, sounds healthy with a nice idle, and revs cleanly. In other words, to all intents & purposes it is as a good Mercedes 4-cylinder engine should be. I think this tells me that fuel pump, fuel filter, fuel relay, fuel distributor, EHA valve, spark plugs, leads, distributor cap, rotor, timing, etc. are all Ok.

2. After a couple of minutes, and as it warms up, the idle starts to hunt up and down, almost stalling but not quite, before revving up again. It also won't rev well anymore, bogging down when the throttle is opened quickly and only revving reluctantly on gentle throttle openings. I've played about with the air/fuel mixture to no avail, and the symptoms are the same whether the air filter is on or off.

It seems that something is not operating as it should as the engine heats up so can anyone make any suggestions? I've thought about vacuum leaks & fuel delivery problems but why would these only appear as it warms up? Any other thoughts would be most welcome.

Thanks,

Andrew