I described the possible relationship leaking valve stem seals would have to your hesitation in the post above. You can live a long time with leaking valve seals, but if the oil accumulates on the top of the piston, it could give you detonation or preignition problems that would cause the ignition to retard under a loan. I don't know for sure if that's the problem, but I believe this is what happened to me and the Techron solved the problem.

I haven't read much about fuel injectors going bad on the 119 engines. I would ask your mechanic if he did a bleed down check on them first before he started swapping out injectors. The injectors expensive ($200 each). If he gets in there and disturbs the engine wiring harness (most of the wiring harness consists of injector wires), you could end up with more problems than you have now.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles