Could be carbon buildup...went thru this with my 500E (same M119 motor). When you first start your car, your electronics set you up with a rich fuel:air mixture until the car's warm. However, carbon in an engine that hasn't run in a few hours is like a sponge (as represented to me by a BG Products engineer) and absorbs much of this fuel, resulting in a lean mixture. And when the mixture's too lean in a cold engine, the engine stumbles.

I used BG Products' "44K", which is specifically designed to clean combustion chambers. After 2 applications, my cold-engine stumble went away.

Just my experience...and by the way, Techron had no impact

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"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo