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Join Date: May 2007
Location: Houston, TX
Posts: 66
Air Leak?

Drove my '91 965 to the car wash this morning and it ran great. Idle AFR between 13 and 14. Tires spinning in second gear...

After getting the car washed the idle and pre boost AFR was at 20! It would drop to approx. 13 when pushing the clutch pedal in and revving the engine to approx. 4000RPM w/o load.

When I got home I heard a faint hissing noise coming somewhere from the left side of the intercooler. Do I have an air leak? If so, how can I identify and rectify it?

Thanks.
Old 07-25-2010, 08:24 AM
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Hello, From the information provided I would recommend inspecting the ducting between the turbo and the air flow meter, In particular the silicon elbow at the turbo inlet, Verify that the plastic tube is engaged properly , I have seen several 965 with similar simptoms and have found the plastic duct partially disconected at this location, Hope this helps,

Lou /AERO DYNAMICS
Old 07-25-2010, 08:47 AM
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Lou,

Thanks for the information. I have another intermittent problem that might be related?

At times the idle RPM stays between 1000 and 2000 RPM and it is apparently caused by the vacuum decel valve. Do you think that the explanation you gave for the air leak would cause the vacuum problem as well?

Thanks in advance.

Patrick
Old 07-25-2010, 09:09 AM
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Hello again, A malfunction on the vac. decel. valve will have no relevance on A/F ratios unless one of its connections is leaking, BTW the aluninum tee on the intake manifold (where the decel. valve is connected) has a rubber plug in the unused port, verify that it is not cracked, You can remove the valve for testing and plug all the connections, Also , does your A/F ratio show the same lean condition condition under boost or is it just under part throttle?

keep a open mind as the two symptoms may not be related, There are several other items that can cause a lean condition,

Lou / AERO DYNAMICS
Old 07-25-2010, 10:14 AM
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I don't know, if it goes lean under boost as I didn't want to cause any damage. However, the AFR was approx. 13 at 4000 RPM w/o any load. Does this make sense?
Old 07-25-2010, 11:18 AM
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