1994 C280 Fast Idle/Cold Start Problems

[mymelt8]

I'm having fast idling problems which after reading some threads on the forum seems to point to the MAS sensor. The engine generally idles at 1000 rpm or so when it's warm and is not under control properly when it's cold. In fact it starts slow and speeds up as it warms up. I had a look at the sensor hopefully and it looks clean. If I disconnect it with the engine running it speeds up even more.
Just occasionally it behaves completely normally when started from cold but will revert to its old self when restarted from warm.Any ideas would be greatly appreciated.