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Running With Disconnected Deceleration Air Valve
I've been having intermittent high idle problems since I owned my 83SC.
It would normally drop back from 2k RPM to 800 RPM if I put the motor under load (slip the clutch a bit at a stop). During a recent trip my idle hung at 2k and wouldn't drop back down no matter what I did. I thought the problem was with my WUR. Meanwhile I mis-identified my deceleration valve as my WUR and disconnected the vacuum line to it. My idle is now rock solid at 800 RPM and I haven't had any high idle issues since disconnecting. Meanwhile I have noticed that I get some burbling/exhaust popping upon deceleration (as expected with the decel valve/vacuum line disconnected). To be honest, it sounds pretty cool. Thoughts on leaving it disconnected for a while? Thoughts on what/where my high idle problem might be? Thanks, Gordo
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Don "Gordo" Gordon '83 911SC Targa |
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03-11-2006, 08:20 PM
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Formerly bb80sc
Join Date: Aug 2001
Location: Hollywood Beach, CA
Posts: 4,361
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Decel valve sounds right, just leave it disconnected. The popping on decel can also be attributed to a lean mixture.
-B
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Cheers -Brad 2015 Cayman GTS 2015 4Runner Limited |
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03-11-2006, 08:51 PM
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Join Date: Jan 2006
Location: Alameda, CA
Posts: 419
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Mine came disconnected, and has been running fine. I believe the reason it was disconnected was so the rpms would drop faster for easier shifting (it has worn synchros).
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03-12-2006, 03:12 AM
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I find the often-repeated comment of disconnecting the deceleration valve to help shifting quite interesting. When working properly the deceleration valve holds engine rpm at about 1,500 to 2,000 for a few seconds then slows to idle speed. This prevents engine stalling on rapid throttle closing. At higher rpm’s it has no effect because the deceleration valve orifice is so small compared to throttle opening. So does this mean these people are shifting down to an engine speed <2,000 rpm and lugging their engines? Why would you heel-and-toe, just let it drop to idle like a rock. Of course you don’t do that. It’s interesting how legends are born.
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03-12-2006, 06:28 AM
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Join Date: Jan 2006
Location: Troy, OH
Posts: 20
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I had the same high idle problem after fixing vacuum leaks. Disconnecting the vac line fixed the high idle, however it does bring the engine speed down rapidly.
I saw a post sometime back about putting a BB in the line. Does anyone have experience with this...or is it just bunk?
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82 SC Targa 00 BMW 540i Sport |
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03-12-2006, 06:53 AM
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Location: Alameda, CA
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Hladun: you've just motivated me to try plugging it in! =)
Babak |
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03-14-2006, 10:52 AM
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Join Date: Jul 2005
Location: Somerville, New Jersey
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Do Motronic ignition systems have a deceleration air valve as well?
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-Matt 1985 Targa |
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03-14-2006, 11:05 AM
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Location: Los Angeles CA
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can someone point out where to disconnect this valve? picture would be great....
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03-14-2006, 11:55 AM
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Location: Alameda, CA
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George nicely modified my picture from when I discovered it on my car:
 The full thread: Idle Now Sounds like a Diesel Truck! Babak |
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03-14-2006, 12:01 PM
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