Check for intake
air leaks
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- Visually inspect intake ducts and duct
joints
- tight clamps
- no splits/cracks/holes
- Visually inspect all vacuum lines and
connection points. Here's a picture
(for a 91, non-TCS)
- no loose fits
- no disconnected hoses
- no broken plastic nipples
- no splits/cracks/breaks
- check all vacuum connections
- turbo bypass line
- turbo boost gauge line
- feed line for both of those, from
manifold
- PCV lines
- fuel pressure regulator line
- evaporative canister line
- vacuum take-off points at the
manifold
- check the rubber grommets for
pliability and a good seal
- Check the turbo bypass valve
- Disconnect the vacuum line from the tee
- suck on the line
- no resistance = bad valve
NOTE: These are my notes from a generic
fuel injection book. I have not done all of these procedures, but they
sound reasonable to me. Corrections and updates would be appreciated.
- Perform propane-injection leak test (if
nothing found visually)
- First, disable the Idle Speed Stabilizer
by clamping the line or disconnecting the electrical connector
- (this is true for '91 and
later; not sure about earlier)
- Fit a piece of tubing to a propane torch
- Preferably, use several concentric
sizes to step the diameter down to about 1/8" I.D.
- Perform the test with the engine cold so
the cooling fan does not come on and disturb the air flow
- Start the engine
- Crack the valve on the propane torch to
obtain a small flow of propane
- Direct the propane toward any
suspected leaks
- An increase in RPM indicates a
leak (Why?)
- Don't forget to check the intake
manifold joints and fuel injector seals
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