I admit that I'm a complete novice. Got my '89 300e because I like driving it and looking at it. Ran and idled great but after new radiator installation (preceeded by some overheating) idles very low and vibrates - just a coincidence? Isn't there a simple fix, like turning a screw or something. I bought one of those CD owners' manuals which is just about useless. Appreciate any advice.

It sounds like a coincidence unless something was altered or damaged inadvertently during the rad install. M103s are very fussy about their caps and rotors, when was yours last serviced? I had an oil seal leak behind my distributor cap that fouled the components and caused a rough idle and in my case stalling. The condition of the plugs and wires should also be checked. What PM service has the car had recently?

Got an oil change; put new plugs in; that's about it in 4 or 5 months.

just some tidbits,
i just bought an 1989 300e with will not start or run problem....bought it with thoughts of parting, got a good deal on parts and good advice from this place, now dirve car daily.......this place isnt god (no typo) but it can give you good advice on how to diagnose and fix problems, and by the way fuel is touchy, check all fuel parts, just an idea