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Rough Running Engine

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Howard View Drop Down
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Joined: 08 Mar 2013
Location: Huddersfield
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Howard Quote  Post ReplyReply Direct Link To This Post Topic: Rough Running Engine
    Posted: 24 Mar 2014 at 2:33pm
My 1988 E24 with just under 60k on the clock has just started to exhibit problems when fired up after a couple of weeks parked in the garage.

Initially, it started and then revved from 1500 to 2500 RPM and back in a continuous sequence. On the road, that translates into a speed of 45 to 70mph in top gear, making it necessary to drive in second and use the breaks to keep the speed under control.
My local expert replaced a temperature sensor related with cold starting, and that seemed to cure the problem for a couple of trips, but then it started again, this time revving from 2000 to 2500 RPM. Strangely enough, it only does it now and again.

Has anyone else had this problem, and if so, how did they fix it?
1988 635csi,
2002 E39 525i, 2001 E38 740i
2003 E39 525i motorsport
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Howard View Drop Down
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Joined: 08 Mar 2013
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Howard Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2014 at 9:58pm
Seems that if I let it warm up for a while, stop it and then re-start, the problem goes away. The chief suspect is the bypass motor which I understand gets gummed up after a few years use (26 in my case) and needs stripping down, cleaning and lubricating.
Job for next week. Will update when I have done it.
1988 635csi,
2002 E39 525i, 2001 E38 740i
2003 E39 525i motorsport
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Robert View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robert Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jun 2014 at 4:49pm
What about the Idle Control Valve? There is an easy test you can do to check the ICV and that is to measure the Ohms between the the centre and outer pins. Each side should be around 20ohm. If either is well below that then it is buggered.

Rob.
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Howard View Drop Down
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Joined: 08 Mar 2013
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Howard Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jun 2014 at 9:38am
Thanks for that Robert. Will give it a try when I have a minute.
1988 635csi,
2002 E39 525i, 2001 E38 740i
2003 E39 525i motorsport
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