knock on E420- any ideas?

[bobjohnston]

I noticed a knocking noise accompanied by a slight burning smell after starting my 94 E420 from cold yesterday, just after I washed it. I immediately shut it down, and checked the oil. Level was fine, the oil looked like new (changed 2500 miles ago). I cautiously started it again, oil pressure was fine, knocking started again, it ran roughly, but gradually started to quiet, so I left it running. It went away completely within 2 or 3 minutes. The knock sounded like it was coming from over the driver's side distributor cap, or front of the cylinder head. I've started it and run it several times since then with no recurrence. Could this be the timing chain or tensioner starting to fail? Or, perhaps a spark problem at the distibutor cap. The knock reminded me of an early rod knock, but doubt that would have gone away and stayed away. The car has 69,000 miles on it and has been well maintained. New distributor caps and rotors were installed a few thousand miles ago. Plug wires are original. Tensioner and upper guides are within my ability to replace, would probably leave a chain replacement to a pro.
Any suggestions re: where to start?

Thanks.

[Edited by bobjohnston on 12-04-2000 at 06:23 PM]

[DSinger]

Before you go to any drastic measures, try a $7 bottle of Chevron Techron fuel additive.

[bobjohnston]

Why the Techron fuel additive?