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do a thorough search for vacuum leaks
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Posted by Monster (more from Monster) on Thu, 19 Jul 2001 09:00:38 Share Post by Email
In Reply to: Weird intermittent stalling/non-starting... 87 900T (long!), ...ethan, Thu, 19 Jul 2001 03:27:36
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Hi, Ethan.

Vacuum leaks can be tricky to find, especially in a turbo. Under boost, a line can split, part, or separate, and it might cause weird problems afterward at idle. Leaks can even be intermittent if a hose unplugs itself and then later gets sucked back onto its connection -- something I've seen on my own car with a loose and hardened old vacuum line.

I think you're only masking the true problem when you disconnect your AMM to get the engine to run. Take a vacuum handpump and individually test each of the vacuum lines on the engine. Carefully check the large fittings (grommets) in the intake manifold after the throttle body, which lead to the brake booster and charcoal canister, and ensure they're tight. I'm betting you find a leak somewhere. A vacuum leak lets unmetered air (the AMM doesn't know how much air is REALLY going in) into the combustion mixture with the result the car runs excessively lean. The end effect might appear to be a fuel delivery problem, but it isn't -- the car starves itself of fuel because the AMM is saying there's very little air going in.

Pat's suggestions to check for spark and fuel pressure are important, but if you find you have both, check for vacuum leaks next.

- = M = -
'87 900T 167K

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