decelration valve cis?

mb911 · mb911's Garage

Ok question. Some of you know I have a problem with my high idle on my 81 sc engine. Here are the symtoms. It starts perfect every time but continues to idle at about 2000-2500 even after it warms up. When warm if I disconect and plug my decelration valve it runs at about 1000 rpm. I have tested the AAR (electrically unit) and it closes after about 90 seconds. It seems to operate fine. The car never seems to have alot of power set up this way. I am replacing the fuel filter this week to try and solve that who knows it may work. any who I read the haynes manual and they don't realy get into the decelration valve and what this means. Please help I don't like being a parts replacer I much prefer knowing what the problem is.

Thanks
Ben

77 911 3.0
75 914-6 2.7

beepbeep · 05-24-2003, 06:15 PM

It is a membrane-device that keeps throttle bypassed for a while when you lift-off the gas to prevent overrich mixture during lift-off and subsequent extra hydrocarbons in the air.

Your membrane is probably shot. You can remove it and plug all three hoses going to it.

mb911 · mb911's Garage

Thanks I will try that. I was thinking that I would have to replace that expensive aav. I hope it works.

Ben

Alan Cottrill · Alan Cottrill's Garage

have you tried to lower the idle when warm, then work out why it won't start/idle cold?

beepbeep · 05-25-2003, 04:49 AM

Deccel valve bypasses the throttle...if there is a hole in it's membrane, air will get past closed throttle no matter what and you won't be able to adjust idle down enough, or you will get funny sideeffects.

mb911 · mb911's Garage

Ok tested the valve and seems good but while I was in there I looked around and low and behold I was adjusting the mixture screw NOT the idle screw. I will give that a shot tommorow as the kids are sleeping now and the car is quite loud with the flowmaster and ssi.

Thanks for your help sometimes it works better to think out loud.

Ben