Chuck/Steve,

I replaced the ignition control module and thought that solved the problem...until I got within about a block of the house and it surged again. Going to work in the morning when it's cooler the idle is constant. Come home in the afternoon when the temp warms up and I get the surging. It's only about 300rpm max, but it's still very noticeable. I'm not getting any relay or black box 'chattering' under the dash and in the footwell, so I'm inclined to rule out those units as a source of the problem.

That leaves me with those other things that have been suggested: idle control valve, temp sensor, vacuum leak, plugs, wires and injectors. From those possibilities I'm inclined to think it might be a vacuum leak...rubber contracts when it's cold and will expand when it's hot. I don't know if that's rational thought or not. I tend to rule out plugs, wires and injectors because it runs and accelerates very smoothly, without any missing. Nor does it have a rough idle. This is the first gasoline engine I've had in about 20 years, so I'm reverting to previous experiences in making that analysis. Perhaps they're not relevant to the SL???

Chuck, is the temp sensor you mentioned previously the brass one that screws into the water pump housing? If not, can you tell me where I ought to look and for what?

The idea that these cars might not run well strikes me as bogus. This thing has run and idled (and still does except for the surging) like the proverbial "Swiss Watch". I suppose that's why anything unusual like this is so magnified.

I hate to throw money at the problem like many seem to do. I've got a couple other 'black boxes' that I will drop into it just to see if I stumble across something that might work.

I appreciate any and all suggestions, and won't rule any of them out. One-by-one I'll check them out and let you know when I finally get it resolved.

Thanks again,

__________________
Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000