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StienbargerR · Joined: 28 Oct 2005 Posts: 1362 Location: Richmond, IN

Min,
Thanks for the tip! I will have to do that soon.

Thanks,
Ryan
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1978 924 NA
-250lb lowering springs, Euro Pistons

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

Smoothie is right - it is the decel valve. If you bypass it you will raise your vac up about 3-5 points hence the quicker idle. But you will backfire and the car will sound like crap. I plan to remove mine after I put in a EDIS system. Until then I just replaced all the lines.
Plug the big lines to and from it if you want to try it removed.
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1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

!tom · Posted: Wed May 30, 2007 3:28 am Post subject:

And how should the hoses be connected to the decel valve?

I've wondered about this myself, since there is a hose connected to the bottom of my decel valve that just hangs down and is open near a bunch of crud in the bottom of my engine bay.
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78 924 NA
5-lug

Smoothie · Posted: Wed May 30, 2007 6:56 am Post subject:

!tom · Posted: Wed May 30, 2007 3:04 pm Post subject:

Well, I connected the small diameter line coming out of the bottom to a vacuum source, there was an unused barb (used to be connected to the A/C) in the big line going to the brake booster.

Once I unplugged the barb and stuck the decel valve line on, the engine idle speed picked up by around 150 RPM or so, and was now idling above 1000. If I revved the engine, it would drop to about 1600 RPM after a minute, and the only way to get it lower than that was to disconnect and reconnect the decel valve.

Something tells me I've got a little adjusting to do. I've disconnected it again for the time being, since it's obviously been tuned to run without the decel valve operational.

First thing I'll do is what Min suggested, and replace all the hoses. Then I'll have to get a pressure tester, set the idle speed, set the timing, etc. so I can get things tuned properly.
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78 924 NA
5-lug

Smoothie · Posted: Thu May 31, 2007 2:38 am Post subject:

I think both of yous have leaky decel valves [or one or both are stickin' open]. They're not supposed to have any affect except when they sense that spike in vacuum when the throttle shuts at approx 1600+ rpm - then it should pop open, then gradually close -completely. One test is to pinch the larger lines shut - if rpms drop then the decel valve is leaky or not closing completely.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox