my 97 E420 runs great, and I'm getting 24MPG on the highway @ 80MPH. However when the car is sitting at idle, the car is unstable, shakes around and the rpm would bounce around. any idea what might be wrong?? again the car is running great when moving..

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Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe