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TurboBert TurboBert is offline
What freekin Oil Leak?
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Join Date: Oct 2002
Location: Oahu
Posts: 177
No Throttle Body Vacuum at Idle

At idle, I have good manifold vacuum but no throttle body vacuum (measured at both the distributor and upstream of the thermo valve, directly at the throttle body).

Anybody know what would cause this?

Here's what I've checked:
1. I have checked for vacuum leaks - none that I can find using an ultrasonic sniffer (has never failed me in the past).
2. The thermo valve is working properly (opens when warm).
3. Manifold pressure (checked at brake booster line) is within spec.

My distributor doesn't advance enough (advances only 15 degrees at 4000). I took out the distributor and checked and it's fine. Weights and springs are good. Vacuum advance on the distributor manually tested fine.

The car accelerates and idles perfectly when I set idle timing to 10 degrees BTDC - spec is 5 degress ATDC. This makes sense because a vacuum would pull this back to the spec value (when warm idle vacuum retard ignition 15 degrees).

'79 930 US
Old 12-19-2004, 11:34 PM
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