Try spraying some brake cleaner around the injectors area...if the idle jumps on it's own, you probably need new injector seals, and/or distribution hoses (not sure of the proper name). I would take the air cleaner off and inspect ALL vac lines for cracks, etc...

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles