BMW 325 revs on startup

Sep 24, 2009 3 Replies
P

My BMW 325 will rev up to 2,000 revs (on a cool day, 1,500 revs on a warmer day) when it is started and drop down to normal tickover straight away.



My thoughts are a temperature sensor telling the ECU that it is a colder day than it really is so give it more petrol and then the ECU realises that is over reving and drops it down. Temperature gauge reads normal (exactly the same as my old 318) so I'm guessing some other sensor somewhere.



Any ideas? Like to get it sorted because I look like one of those people who scream their engines on start-up.



Regards


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M

basic stuff first: check the throttle cable (if it has one) is not too tight and run a general check over for vacuum leaks

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D

With an injection engine if you 'give it more petrol' it will run rich and stall. More air makes it run faster. So I'd be looking at the idle control valve or for air leaks into the plenum.

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P

Thanks to you and MrCheerful.

Had a browse round and found a disintegrated vacuum hose. So much so that I can't even see where the other end of it should go. I'll have another look in daylight or enlist the help of a friend who's just done a rebuild on the same engine. He should remember where it should go.

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