It appears the thrust cutoff switch was indeed the culprit. I will know for sure after my afternoon and evening drives.

Since installing the new one last night, I have maintained a constant 550 rpm in drive and in neutral, and engine thrust is definitely cutting off when I lift off the accelerator at higher speeds.

I have also noticed that, once warmed up, my acceleration is a lot peppier than it has been for the past year or two. Normally, on moderate to hard acceleration, I rev to 4000-4500 rpm before the car shifts. Now I am seeing 5500, and the engine pitch is also higher – like it was when I got the car. I assume the engine is breathing easier now, and am surprised that the thrust cutoff switch has such a significant impact.

I am also still running lean (and have been for about two years), which I assume is the reason why, on soft acceleration, there is a slight lag before the engine spins up – almost like a turbo lag. I suppose that will clear up once my fuel/air mixture is adjusted.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black