I'm working on my daughters 1990 190e 2.6ltr.We are having idle problems.The car at first would idle real high(1500 rpm) whenever it felt like it.Cold or hot didn't seem to matter.Yesterday it was fluctuating up and down quickly.With the fluctuation was a "clicking" sound,it would click and the idle would go up, then click and the idle would go down.It sounded like it was coming from under the air cleaner,or at least thats what I thought.Buy the time I got the air cleaner off the idle smoothed out and was fine and the clicking was gone.The only other symptom I noticed was that the fuel pump was much louder than normal,very high pitched whine.We have had the car for at least a year and the pump was never this loud before.One more thing,this all started after a routine oil change and a pressure washing under the hood.Thanks in advance,Chris
(learning mercedes the hard way)

Pressure washers tend to force water into places that weren't meant to have water in them. Was an actual pressure washer used or did you give it a spirited squirt with a garden hose?

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Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles