Yet another 300E idle problem
 

My 1990 300E-24 has an idle problem (so whose hasn't). At cold start everything is ok but as soon as the cold start valve closes after 12 seconds or so it cuts straight back to normal idle, ie there is no fast idle. However, once the engine warms up it settles into a 1000-1100 rpm idle. During a warm start it settles into normal idle, c700 rpm, for a couple of seconds then quickly climbs up to the higher mark in the next second or so. As a first step I changed the ovp relay today but it made no difference. Any ideas please.
Cheers
Brian