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Old 11-28-2012, 08:03 PM   #1
Barry
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Surging engine at idle HELP

So I got the engine rebuilt. I have the transmission swapped out for a 5 speed. A new gas tank. All good things, except now the darn engine surges between 1700 and 2300 RPM when I start it. I have changed the idle control valve and the MAF, no difference. If anyone has any ideas please pass them on thanks.

!990 325is m20
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Old 11-28-2012, 08:58 PM   #2
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Just surges once when you start it, or stays there when at idle?
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Old 11-28-2012, 09:20 PM   #3
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It continues to surge until you shut it off
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Old 11-28-2012, 09:36 PM   #4
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Likely a vacuum leak somewhere. There is a line under the throttle body that goes to the vent line on the gas tank, maybe that got left open?
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Old 11-28-2012, 11:22 PM   #5
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I have checked the line under the throttle body.
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Old 11-28-2012, 11:32 PM   #6
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Definitely sounds like a vacuum problem. Check all the hoses?
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Old 11-29-2012, 07:18 PM   #7
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I don't believe it is a vacuum problem. I have checked the ICV and the power source no power on the centre terminal ( battery voltage should be present), So before I rip the wiring harness apart, is there something else I should be looking at?

Thank you for the suggestions so far.
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Old 11-29-2012, 08:30 PM   #8
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It sounds a lot like the vacuum hoses! I had a very similar problem and upon changing the hoses (thanks to 5style) my revs stabilized drastically.
The hoses on my car had never been changed, so when I replaced them they had several holes and tears. Have you checked the condition of the vaccum hoses underneath the ICV? Those apparently are also pretty integral to stable revs at idle. GL and hope that helps!
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Old 11-29-2012, 09:43 PM   #9
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Ok SO here is where I get to eat crow. I went and pulled each vacuum hose and checked them all individually. There was a small crack in the line that goes to the break booster. I could have sworn I replaced all of the vacuum lines. So thank you everyone The surge is gone.
I still have a check engine light that says the ICV is acting up but at least she runs.
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Old 11-29-2012, 11:02 PM   #10
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good stuff. Good luck with the ICV!
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Old 11-30-2012, 01:52 AM   #11
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Yay! Good work!
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Old 11-30-2012, 10:34 AM   #12
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ok, I'm gonna thread jack here: I just rebuilt the top end of a M20 and the idle races to 2k and stays there. Tried reving it to drop but it doesn't seem to go down much. I unplugged my AFM and the idle drops with the dme trying to compensate so the car runs a bit rough. She stabilizes after a min or so. The car stays running with it unplugged.

would anyone know what the possible cause of the high idle could be?

any help would be appreciated. thx.
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I think I've had 14 bmw's in 4 years.
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2 325i 4 dr - sold
4 318is all white - sold and parts
1 87 325is red - parts
1 89 325i vert grey - parts
1 90 325is white - keepin
1 87 325i vert -red - keepin
latest addition 1 88-325is red - parts
latest addition 1 89-325i vert - white -fixin/sold
latest addition 1 92-318i vert - blue - parts
latest addition 1 87 325is blk - parts.

latest addition as of 2013-Gold 87-325is auto! it's a keeper!
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Old 11-30-2012, 12:06 PM   #13
TSI
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Quote:
Originally Posted by Ceeker View Post
ok, I'm gonna thread jack here: I just rebuilt the top end of a M20 and the idle races to 2k and stays there. Tried reving it to drop but it doesn't seem to go down much. I unplugged my AFM and the idle drops with the dme trying to compensate so the car runs a bit rough. She stabilizes after a min or so. The car stays running with it unplugged.

would anyone know what the possible cause of the high idle could be?

any help would be appreciated. thx.

ICV? T-stat?
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Old 11-30-2012, 02:44 PM   #14
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no a thermostat wouldn't cause that - that's a cooling issue. I've swapped out the ICV and nothing changed.
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I think I've had 14 bmw's in 4 years.
2 IX's -sold and parts
2 325i 4 dr - sold
4 318is all white - sold and parts
1 87 325is red - parts
1 89 325i vert grey - parts
1 90 325is white - keepin
1 87 325i vert -red - keepin
latest addition 1 88-325is red - parts
latest addition 1 89-325i vert - white -fixin/sold
latest addition 1 92-318i vert - blue - parts
latest addition 1 87 325is blk - parts.

latest addition as of 2013-Gold 87-325is auto! it's a keeper!
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Old 11-30-2012, 03:54 PM   #15
TSI
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no a thermostat wouldn't cause that - that's a cooling issue. I've swapped out the ICV and nothing changed.

I had a friend who had that problem for a bit. Can't remember the details, but the T-stat was stuck, basically telling the engine it was too cold and increasing revs as a result.

Maybe he's mistaken, though. Not the brightest bloke.
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