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Old 12-03-2012, 06:57 PM
QAfred QAfred is offline
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Location: Panhandle of Florida
Join Date: Aug 2008
Posts: 919
Mein Auto: 328i, 330ci, R1200C
Originally Posted by 1972ford View Post
I've been chasing an idle surge problem for a few weeks now, although it's hardly been a priority. It's gotten cold out here in NH and I feel like it is related to the temp, but can't say for certain. The car starts normally and idles perfectly cold, then after a short drive e.g. to work, when I clutch in the idle fluctuates from 500 to 1000 and back about 8 to 10 times and then settles down to 700ish, and stays there.

I have cleaned the DISA valve and ICV and replaced both intake boots. The ICV in particular was quite dirty, and the lower intake boot was definitely cracked, but the problem is more or less exactly the same.

My research has pointed me to look for vacuum leaks, but other than visual inspection of the hoses I can see, any thoughts about how else to pinpoint a possible leak?

Thanks in advance.
Pull the lower vacuum line off the F connector from the intake boot just behind the MAF. There should be a 4 inch piece of 3.5MM vacuum line and about three feet of hard plastic line and then another 4 inches of vacuum tubing where it attaches to the fuel pressure regulator. You may have to cut the vacuum line off the F connector, if it is old and brittle etc, so have some on-hand to replace it. Blow into it and make sure that line is solid / no leaks down to fuel pressure regulator, or you can pull a vacuum on it if you are shy .

Anyhow, that is how you can check that one without jacking up the car and removing fuel filter cover etc. I would also recommend you change all the 3.5MM vacuum line from secondary air pump where it wraps around intake manifold and goes into vacuum switch behind intake, back out to check valve and back into the intake. Vacuum switch is easily detached to make job much easier. There is also a cap/plug back there that can crack.

Check out post six on this link to see what I am talking about.

Last edited by QAfred; 12-03-2012 at 06:59 PM.
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