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Revs Dropping slowly Part 2.....HELP!!!

Hey guys i was just looking over this thread......Revs drop slowly when changing gear ... why?

I am having the EXACT same problem that BILLJAM had (REVS DROPPING SLOWLY WHEN I LET OFF THE THROTTLE) , if i understood correctly he solved it by removing the Vacuum limiter valve. So far i have replaced the compressor bypass valve with a new one, removed intercooler and checked for hose leaks and i made sure the butterfly valve was opening and closing correctly.
Now before i buy another vacuum limiter valve.... i want to know if this sounds right... I could not blow any air through the valve and when i put a vacuum on it it would start to open at 16 to 17 psi. Somone else told me that it should open at about 23 psi. Do you guys know what that value should really be??? It would hold a 35 psi vacuum without leaking so i dont know if this thing is bad or not??? Anyone have any ideas???

Thanks
JERRY
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Last edited by boeing 717; 02-07-2009 at 12:25 PM..
Old 02-07-2009, 12:22 PM
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Disconnect the hose from the outlet of the valve and cap it off. Now your done.
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Paul B.
'91 964 Turbo
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Old 02-07-2009, 01:57 PM
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Heh... thanks Paul will run it like that and see if its better.

JERRY
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Old 02-07-2009, 02:01 PM
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Jerry, I saw your original post on Rennlist (we Pelican'ers tend lurk on both forums). I think Paul's direction is good...take the damn thing out of the equation and see what happens. The first step in troubleshooting.

JFairman knows his stuff, and as to whether 17 inches of vacuum (or 23 inches) is where it opens, what was quoted is most likely a Porsche part specification...and/or experience talking. Yours might be opening a bit sooner than intended, causing your rpm's to hang up more than they should. Let's see what disconnecting it does for you. I stll have my vacuum limiter connected with no problems as you've experienced. But what you learn, so shall we all!
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Old 02-07-2009, 03:05 PM
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Thanks Mark, im gonna disconnect it to see if thats the problem but i really dont want to leave it off id rather just replace with a good one. When i get this solved ill post it as well.
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Old 02-07-2009, 04:22 PM
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Jerry,
I have since deleted almost everything from my engine that I can get away with. Fortunately, I never have to worry about low temperatures even in winter, so all of the cold start aids have been removed.
I have revised the factory diagram (copied from the back of the Owner's Manual) as I removed parts just so I could keep track of things for trouble-shooting.
Below is a copy of the standard system diagram and the diagram below that is where I am now. This is for a US 1986 930.
I have a B6 intercooler and small BOV which replaces the original large blow-off housing (19).
I don't have any problems with starting, idling or general running, although lifting off the gas a little at high boost brings on engine braking a bit abruptly sometimes, however I am getting used to it now and compensate with my right foot accordingly.
I hope this is of help.



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Old 02-07-2009, 07:34 PM
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Jerry, there's no reason other than emissions to have that valve hooked up.
Once you drive your car and don't have to wait 3 seconds to shift (the turbo is slowing down during this wait) you won't want to hook it up again.
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Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 02-08-2009, 04:50 AM
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Thanks guys....Ran perfect with that valve off. I suppose i need to hook it back up though before i have my emissions done, would that be true??

Thanks for you help....
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1992 968
2011 Cayenne
2007 997 Turbo
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Old 02-08-2009, 10:13 AM
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