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Registered User
Join Date: Mar 2009
Posts: 134
CIS cold idle

911 SC Euro, non-lambda - now idles horribly. At start up, it fires up, then sputs and sputters until it dies. It will do this several times. After some heat builds up, it can keep a rough idle. Or, I can keep it going by applying some throttle.

Under power it is better if not fine. Just idle is horrible. Even when warm, its pretty bad. The engine may even die if I don't give it some throttle to maintain idle when warm.

It occasionally backfires out the intake (via the pop-off valve) during cold warm up.

The car idled fine in the summer, haven't started it again until recently - now the horrible idle.

What changed? During the months of disuse, I replaced the front sway bar, which means removing the gas tank. I drained the tank via a hand pump via the level sensor opening. You might think crud or gunk collected in the tank somewhere, which would restrict fuel pressure and flow. However, if that was the case, would it run better when warm and ok under high load conditions?

I have checked system and control pressure which is 5.1bar and 1.7bar respectively (really cold). After a minute or two, control pressure is 3.0bar.

I've checked the auxiliary air valve and I can see that it is partly open by looking into its outlet.

I believe the cold start injector is working, because it always cranks and fires quickly... it just can't maintain the idle.

I'm not sure what to check next.

Old 10-15-2012, 08:27 AM
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T77911S's Avatar
Join Date: Oct 2006
Location: MYR S.C.
Posts: 13,771
check for air leaks since your FP's seem to be fine. make sure the pop off valve is closing. they can get unhinged and let air in.

ignition- cap, rotor, plugs, wires.

the engine should idle up when cold. ,make sure the AAR is clean and not stuck. they can get stuck and not open when cold.
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Old 10-15-2012, 08:30 AM
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Designer King
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Join Date: Mar 2004
Location: Toronto, ON Canada
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You didn't say where you are located. What was the ambient temp for the cold start test?

Aside from what Ty said about leaks and ignition, have you verified your mixture (CO%)? Backfiring through the intake usually means a too lean mixture.

I'm not sure if this would affect your pressures, but make sure the small filter @ the top of the WUR is not clogged.
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Old 10-15-2012, 09:56 AM
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Vereeken's Avatar
Join Date: Mar 2004
Location: Belgium
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1.7 bar on a EURO SC is high when your "really cold " means exactly that (temp below 10 celcius.) Ofcourse for all I know you live in Florida and you think that 20 degrees is cold ;o)

Also your warm cp after a couple of minutes is 3.0 bar. If you know that the Thermal valve opens after 45 seconds and increases the controle pressure with roughly 0.6 bar that means that the bimetal has added 0.7 bar in pressure in a minute or two which seems about consitent with my observations on a 089 WUR.

So where do you live and what was the outside temp when you measured the 1.7 bar?
My dad always found an excuse why not to buy a Porsche, so I guess I am all out of excuses.
Old 10-15-2012, 12:49 PM
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Registered User
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I live in Kansas City. The temps when I've started the engine have been from 40 deg F up to the 60's. The 1.7bar control pressure was when it was in the 50's I believe.
Old 10-17-2012, 01:30 PM
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The Mighty Pieholio
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Join Date: Nov 2007
Location: North Canton, Ohio
Posts: 17,271
Originally Posted by Vereeken View Post
1.7 bar on a EURO SC is high
Vereeken hit the nail on the head.

From the attached link you are way lean. 1.2 bar is where you should be at 50F with an 089. This is not a factory graph but I think you have some good info for to dig into this.

WUR specs2

Spring for a pressure tester and it will set you free. There are some awesome threads here on how to adjust both cold and warm pressure.

1981 911SC Targa
Old 10-17-2012, 02:32 PM
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