Vacuum issue – I need some new ideas

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06-21-09, 09:09 PM

moehler

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Vacuum issue – I need some new ideas

I am having a difficult time diagnosing a vacuum issue and was wondering if anyone can help with some different ideas. First off, my vacuum has always been on the lower side; -320/-330 on the PFC at 950 rpms. But last week I looked down and it was at -280/-290 and it hasn’t moved much since then. The engine made great compression two months ago 110 psi/114 psi, and nothing dramatic has happened since. Car starts up warm or cold with no issues.

I also noticed that during this time is that after a hard drive (redline pulls) the idle sits at about 1300-1500 rpms for about 30 or more seconds before settling down to 950 which it holds. Normally this takes seconds.

I have checked and re-checked the vacuum lines (car has a single turbo with only about 10 lines) and couplers and they all look good. Today I sprayed carb cleaner everywhere I could think of and did not notice anything.

One more piece of information that may be related. Since I’ve had this car in November, the boost as read from a manual gauge (two different ones now) from the UIM nipple shows a lot of fluctuation at WOT. The PFC reads no fluctuation. This bothered me, but I have been ignoring it. I am starting to think this is all related.

Any idea what I should look at next? Has anybody had a similar issue?

Thanks,
Matt

Last edited by moehler; 06-21-09 at 09:10 PM. Reason: spelling

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06-21-09, 10:10 PM

IRPerformance

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Bring the car by my shop if you like and I will set it straight. The idle sticking is most likely a tuning or mechanical issue with the throttle body.