Leaking intake?
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Teching In
Joined: Mar 2010
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Leaking intake? 5.3 with ls6 intake. starts and idles fine but at part throttle it surges up and down, not steady. I have taken it on short runs around town and at stops it wants to die. AFR at idle is 15.5-16 or higher, gauge only goes to 16. When i shut it off there is a loud whistle, sounds like air. Is my intake leaking? 
12 Second Club
Joined: Mar 2005
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From: Corpus Christi
spray carb cleaner around the intake/tb mounting surface. pay attention to where the idle increases as where your spraying. thats where you are getting a leak. no idle increase no leak...........
Above are all good statements. I would check for vaccuum leaks everywhere and definitely if there is a way for you to put a thin paper strip around areas where you think it is leaking (in a garage preferably so no wind will hinder your results) this might tell you if the strip blows it is an area where there is a leak. I've heard of guys using soapy water around the areas (no electric components or they are taped up well) and wherever it bubbles it will be a tell tale sign of a leak. Could even be a bad gasket material..... So many things to check. I wish I had an easy answer for you. Good luck.
Thread Starter
Teching In
Joined: Mar 2010
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thanks for advice, today i tried the carb cleaner trick and did find a leak at front of intake so i retorqued fasteners and that spot seems OK now but at shut down it still sounds almost like unplugging a hose from a compressor. no noise while running
