Alterntor problems with c300
Thread Starter
Newbie
Joined: Mar 2015
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2009 c300 4matic
Alterntor problems with c300
Hi I recently replaced my alternator in my 2009 c300 4matic and when I turn my car on it revs up and down for the first couple of seconds which is strange, my mechanic says its normal it will go away with a few kilometres of driving.. I am not convinced and my car still shakes a bit. Does anyone have advice for me or tell me what it could be?
Senior Member
Joined: Jan 2013
Posts: 344
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From: Berkley, MI
'09 C350
I had mine done under warranty last year and none of this was happening. Are you saying that your RPMs are jumping during start up? If so is the CEL on? I think your mechanic forgot to plug something in when he was doing the job. Most likely a vacuum line somewhere, or a sensor.
Thread Starter
Newbie
Joined: Mar 2015
Posts: 2
Likes: 0
2009 c300 4matic
Yes, it only does it at start up and my cel is not on at all. It goes up to 3000 rpm but the mechanic said that because you need to start it up a couple of times and because it's cold the computer will eventually adjust to it and eventually it will stop. I hope he's right, it's only matter of time that I will revisit him again to get this dealt with. It is really cold up here in Toronto so you thinks he's right? Is it simply because it's cold? Thanks for your reply!
Senior Member
Joined: Jan 2013
Posts: 344
Likes: 2
From: Berkley, MI
'09 C350
I'm not a mechanic, but have never heard of computer having to "adjust" to anything after an alternator change. The alternator is a mechanical part and the usually when you replace it, the battery should be disconnected which in itself should "reset" the ECU. If your CEL is not on, you can go with his suggestion and see if it goes away, but I would still be a little weary that something's not right.
