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DailyDriven'88 DailyDriven'88 is offline
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Join Date: Aug 2008
Location: CA
Posts: 181
Originally Posted by JFairman View Post

A rich idle mixture in a fuel injected car will always cause the rpms to oscillate up and down and thats a fact.
I have never experienced this with a carburator running rich at idle though.

An air leak after the turbo and before the throttle butterfly, or blow off valve will be a pressure leak at all times other than when you first snap the throttle open before the turbo spools up.
The turbo is making pressure in the intake before the throttle body at idle and steady cruise, it's just low enough to not show on the boost gauge.

This is metered air so if any is leaking out between the turbo and the throttle body it will cause a rich mixture.

Have you tried lowering boost control pressure with your Brian Leask adjustable warmup/control pressure regulator yet?
I have also experienced on some electronic FI cars where a vacuum leak will cause a surge/oscillation at idle and if you combine that info with a rich condition on a carb'd engine not causing the issue, that just shows me just how different many of the systems out there respond to different situations. Thanks for the clarification.

You got me thinking about an air leak after the turbo but before the throttle plate. I have new O rings throughout but what if the BOV isnt sealing tightly? I put in new seals about 6 months ago but I did happen to hear a ticking noise from that area the other day (not while it was surging). It sounded like the recirc valve spring inside rattling. I havent heard it since. I may throw new seals in there again for the hell of it.

Jim, have I been mis-reading this whole time? Are you suggesting raising warm cp or boost cp? I thought warm cp. The car does have the rpm switch so how would boost cp have any effect on idle? I can see how it would be possible if I didnt have the switch.

Mark: I did bypass the 2 switches inline with the dizzy vacuum lines and no difference other than a lower and rougher idle during cold start. I will probably hook them back up.

Last edited by DailyDriven'88; 10-23-2009 at 03:23 PM..
Old 10-23-2009, 03:19 PM
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