Mercedes dealer changed the coil to plug connectors. Service manager sketched the coils with the connectors and the bottom connector is the one which goes bad. Hopefully the Tech replaced the right ones, about $14 each and $20 labor. All three coils were done.

That idle condition seems to be better.

Since I was there, I had them change the oil as well, they had Mobile 15W40. Next oil change I will go back to 10W30.

I cleared all the codes, and checked them a few days later. Still getting code 13 (mixture too lean or rich).

What can be checked next. MB has added a layer of complexity for emissions controls. Some choices like delayed transmission shift can have adverse effect on a cold engine.

Again, it drives fine at all speeds, like a new vehicle.

Is it possible for the secondary air injectors to keep on running even after warmup, causing the lean mixture?

Some time back, after some hill climbing and decent, I had code 20 (mixture too lean or rich at idle or partial load) but that has not returned since. This was before the fuel injector cleaner, connector and oil change. Two other DM codes I had were code 3 (lambda inoperative) and code 4 (air injectors inoperator), along with 19.

Speedo needle vibrates a little below 40 MPH, can that have any effect?

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Zafar
94 E320 58000 Miles