cold running

Hi I'm looking at a UK 1988 300SL for a friend. He has a cold running problem ( tick over at 500RPM) He's changed the cold start valve still the same... it has a feed I have put a feed across the idle control valve and runs better I need the following info 1. a Wiring Diagram...

C220 Cdi 2003 (W203) Winter's approaching and I'm not prepared to put up with the cold running of the C220 anymore, and before everyone chimes in with, "it must be the stat"; it aint. I thought it must be the stat too, so at the last service I got the garage to replace it, but it made no...