How big is the fluctuation in engine speed? Slight fluctuations of around 10-20 RPM are normal, my M104 has always done it at idle. I don't think this is any cause for concern.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record