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-   -   Surging engine at idle HELP (http://www.maxbimmer.com/forums/showthread.php?t=154654)

Barry 11-28-2012 08:03 PM

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.:mad: If anyone has any ideas please pass them on thanks.

!990 325is m20

TSI 11-28-2012 08:58 PM

Just surges once when you start it, or stays there when at idle?

Barry 11-28-2012 09:20 PM

It continues to surge until you shut it off

everlast 11-28-2012 09:36 PM

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?

Barry 11-28-2012 11:22 PM

I have checked the line under the throttle body.

TSI 11-28-2012 11:32 PM

Definitely sounds like a vacuum problem. Check all the hoses?

Barry 11-29-2012 07:18 PM

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.

BostonGreen 11-29-2012 08:30 PM

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!

Barry 11-29-2012 09:43 PM

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.

TSI 11-29-2012 11:02 PM

good stuff. Good luck with the ICV!

everlast 11-30-2012 01:52 AM

Yay! Good work!

Ceeker 11-30-2012 10:34 AM

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.

TSI 11-30-2012 12:06 PM

Quote:

Originally Posted by Ceeker (Post 1590958)
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?

Ceeker 11-30-2012 02:44 PM

no a thermostat wouldn't cause that - that's a cooling issue. I've swapped out the ICV and nothing changed.

TSI 11-30-2012 03:54 PM

Quote:

Originally Posted by Ceeker (Post 1590977)
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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