Chuck,

I made some progress this afternoon. I pulled the filter housing off and began looking for vacuum leaks. I immediately came across a vacuum line that had somehow become disconnected. There is a green and yellow vacuum element to the right of the idle speed control valve with a long l-shaped vacuum hose that attaches to the manifold. The hose had broken down and somehow gotten pulled off. I can't imagine how that happened. Regardless, I just happened to have one of the fittings and stuck it back on.

We drove the car to dinner over in Destin, which is about 15 miles. I pulled into the parking place, put it in Park and sat for a couple minutes. It still surged a couple times, but only about 100 rpm. Same thing when I got back to the house. Nowhere near as pronounced as it had been, but still slightly there.

Now, I don't know if there is a 'memory' that has to be overcome or not. Though the car is not one of our daily drivers, I'll drive it daily for a week or so to see if the idle smooths back out.

I appreciate your, and everyone else's, help in trying to run this to ground. This is a terrific forum, with a wealth of information available and people willing to put themselves out for others. I've bookmarked this thread and will use the suggestions if the problem persists.

Again, my thanks.

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