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B. Elliott's Avatar
 
Join Date: Jun 2006
Location: Pearl Harbor, Hawaii
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Won't idle / super rich

I just got everything back together and tried to start her earlier. After charging the battery and trying to start it she immediately backfired and separated the intake manifold... Found a couple of plug wires in the wrong spots on the lower drivers side bank. Fixed those and then got the manifold back together.

Second try and primary issue; She will turn over and starts almost perfectly, but refuses to hold idle and runs VERY rich. I can give it a little gas and it idles ok as long as I'm holding it. As I slowly take my foot off the gas it just drops and dies. I disconnected the O2 sensor completely and it runs a little less rich, but still rich nonetheless and won't idle.

Could the backfire have blown out my fuel regulator?

The vacuum line from the regulator is running to the three-way T where one routes to the intake manifold below the throttle linkage, while the other routes to the cutoff valve... Appears to be setup fine.

Any suggestions? (please help!)
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'90 964 C4
Old 01-23-2012, 08:51 PM
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Eric
 
Join Date: Apr 2009
Location: Brisbane, Australia
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Not sure what you changed when you pulled it a apart, but you should first check all the vacuum lines are in place.

The Motronic and fuel injection system the 964 uses is similar to that on the 944S2. Basically idle maps do not have O2 feedback - they are a fixed pulse duration (no adaptation) with adjustments for air temperature and engine coolant temperature. The DME adjusts the idle by the idle control valve which controls the bypass of air past the closed throttle body. More air = leaner, less = rich. It sounds like your ICV is either stuck closed or disconnected somehow.

I would suggest check the electrical connection as a minimum and also check all pipes. You should also check your AFM is connected as it used the AIT in this to determine idle fuel - although this is less sensitive as it defaults to about 20 degrees IIRC.

Also check the FPR (as you suggested) as I suppose it is possible that the excess pressure from the backfire damaged the FPR through the vacuum line connected to it. In which case you would probably end up with excessive fuel pressure and a rich condition. Off idle the DME can compensate to a degree through O2 adaptation.

Good luck.
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Eric

Last edited by Eric_Oz_S2; 01-24-2012 at 01:53 AM..
Old 01-24-2012, 01:48 AM
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Was it running fine before you worked on it?

1. If it does not want to idle, check to make sure the idle switch on the throttle body is making.
2. Go through all the vacuum lines and make sure they are all secured and seated. You have to remove the airbox or do a partial drop to get a better view of the backside of the engine compartment.
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2011 Silverado for hauling (35k miles)
Old 01-24-2012, 02:38 AM
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I don't know to what extent you had everything apart, but did you happen to stuff some paper towels into the intake tubes and forget to remove them? That would get you a rich mixture.
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Alex

1995 Carrera 2 - Speed Yellow - Alps Touring
Old 01-24-2012, 10:29 AM
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Thankyou for the input guys! Last night I inspected my idle control valve and it was stuck solid. I'm ordering one tonight so that I can at least have a good idle to diagnose from... if that isn't the only real issue.

Thanks again!
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'90 964 C4
Old 01-24-2012, 06:23 PM
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