What part makes that whirring whine at startup? Fuel pump? It kicks in soon after you start the car, and if you don't drive off, usually stops after 30 seconds or so. The reason I ask is I have an engine that drops revs when idling for a while after startup, and this morning when it did it, the vaccuum-cleaner noise kicked in very briefly after I had driven a mile or so and was stopped at a light, when the revs dropped. I'm trying to find a correlation.

Sounds like the airpump to me.

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2007 C 230 Sport.

What the heck is an air pump?

It is part of the emissions control system. It is the little black thing below the alternator that doesn't have a pulley on the front. Last time you mentioned this problem, I said I had the same thing (but not as bad) on my 98 C230 and that I thought it was something to do with the emissions control system. Sounds like maybe I was on the right track. Unfortunately, I don't know any more than that. Maybe someone can suggest how the air pump operation could produce these symptoms. It seems our symptoms are both these: After driving a short distance, when coming to stop at a light, after a few seconds the RPM's suddenly drop below 500 and then recover. Is that it?

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

That's it.

Well, we both have the same thing. How bad is yours? I hope someone can tell us if it is normal or what can be done about it.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Normal I believe. That pump runs almost immediately after a cold-start, and I believe is programmed to run 2 minutes. Then it's off. That's when the pump is actually doing the job it's supposed to do. THEN later on (when the conditions are just right) the pump will come on again for a very brief period. The engine computer is testing the air pump, it can see the change in the O2 sensor,so it knows it works OK.

Gilly

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Sounds good to me Gilly.

Any ideas on the RPM stumble?

That's the reaction to the sudden load increase the pump places on the engine.

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

Wellll..........

All fine, except the noise (which we have ID'd as the air pump) is a secondary question. When the motor is cold, at idle (stoplights) for a few miles after initial drive-off, the RPMs go up and down constantly. That is not normal, and I had wondered if there was a correlation.

I don't think it's related, unless there is something weird going on between the air pump and egr valve, like if some wiring got mixed up. Is there any recent service work done to the car? I don't buy the "sudden engine load", not with this electric pump. (have computer checked for codes)
Other than that, maybe the throttle actuator going bad.........tough one. These driveability concerns can be a real bear.
Gilly

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Click here to see the items I have up for auction at EBay

Click here to see a photo album of my '62 Sprite Project Moneypit (Now Sold)