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Loosing Vaccum when Brakes applied.

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Old Sep 12, 2011 | 07:35 AM
  #1  
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Default Loosing Vaccum when Brakes applied.

Well like it says.. Just rebuilt the engine, put in a 228r cam and longtubes. Had it tuned but they were having a problem where when idleing in gear and coming to a stop with the brakes applied the car will start to buck and jump. and slowly loose vaccum climbing almost all the way to atmosphere pressure. then when you take your foot off the gas it sputters and spits till it builds again.. We checked the vaccum lines, and clamps and replaced the MAP. and cant figure out where its coming from.. Where should i look. I have a spare intake the tuner gave me im thinking im going to swap it out. maybe i have a hairline crack in mine somewhere. Thoughts?
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Old Sep 12, 2011 | 09:45 AM
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Ohh BTW this is on the Camaro. Fresh Rebuild. 228r cam and LT's.
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Old Sep 12, 2011 | 10:07 AM
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May be a bad brake booster too. Apply vacuum to the booster only and see if it holds it.
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Old Sep 12, 2011 | 10:54 AM
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sounds like the diaphragm in the booster, or the check valve.
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Old Sep 13, 2011 | 03:43 PM
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checked the Check valve. its working. and when i pulled the check valve the booster had vaccum in it.. So im not sure whats going on.. I did notice that when i had the engine running and i put my hand over the vacuum hose going to the intake it didnt have as much "suction" as i thought it had previous to the rebuild. The Map shows 60 ish when idleing.. But as soon as i start pumping those brakes idle drops and vacuum climbs.. 70. 80. 90..
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