1987 BMW 325

JSK56

MEMBER
1987 BMW 325

Computer problem
1987 BMW 325 6 cyl Two Wheel Drive Manual

Engine starts fine, idles up-cold run, then starts to surge at idle from 750 to 1500. Sounds like someone is turning the key off and on when rpm rises. Engine operates normally at highway speeds - the problem is only present at idle.
Any ideas would be greatly appreciated. Thank you.
Jeff

The engine is a 2.5 L6, fuel injected

5 Replies

DOCHAGERTY

MECHANIC
9,601 POSTS

It will possibly require replacement of the idle control valve and idle control unit and checking the throttle position switch. The engine in an ETA car is 2.7 liters.

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Saturday, March 28th, 2009 AT 8:43 AM

JSK56

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6 POSTS

I forgot to say that this problem only started after replacing the crank sensor - or pulse generator as BMW calls it. I replaced the original crank sensor with an after-market sensor. The lead on the after-market sensor was shorter than the original, so re-routing the lead was necessary. I then replaced that one with a BMW sensor which had the correct length lead. Still the surge problem. Engine idled fine before changing the original sensor - has had problem ever since. The timing of the problem with the changing of the sensor seems suspect to me - but it also could just be a coincidence. Thank you again for your help.
Jeff

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Saturday, March 28th, 2009 AT 2:46 PM

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What was the reason for replacing a good crank sensor? Also what are the last 7 characters of the VIN?

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Sunday, March 29th, 2009 AT 2:27 AM

JSK56

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6 POSTS

The original crank sensor went bad - no signal. That's why I replaced it. The surge problem started after I installed the after-market sensor with the short lead. That's why I replaced the after-market with a BMW part - I thought maybe the after-market one wasn't exactly right and might be causing the surge problem. But the surge problem was still present after I installed the BMW part. The last seven of the VIN are: 8831325. Thank you.

Jeff

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Sunday, March 29th, 2009 AT 3:06 PM

DOCHAGERTY

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Alright, the issue here could well be a sticky idle control valve as the I motors have the idle control integrated into the engine management. Try cleaning the ICV and see if it helps.