Finally about to get to the bottom of what was causing the stumbling on start-up. I replaced the fuel filter, fuel accumulator, injector seals, insulators and o-rings, fuel pressure regulator on the back of the CIS and the idle air circulation hose...all to no avail.

Turns out there were at least two injectors bleeding down. Replaced one on the right side of the engine and the stumbling was reduced by about sixty percent. Still need to replace an injector (maybe two) on the left side of the engine and I expect this to cure the problem.

Replaced a lot of parts trying to run this to ground. All of them, except for the fuel accumulator, had never been replaced. So, after 140,000 miles, it was probably about time. In the process, I might have saved myself some headaches down the road.

In retrospect, I should have replaced the injectors at the time the seals and insulators were replaced. Wouldn't have cost any more in labor beyond the $200.00 that I paid. Just another $250.00 for injectors. I may go ahead and do that anyway.

Hope this helps others with a fairly common problem

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