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vacuum leak

12K views 9 replies 5 participants last post by  travispett 
#1 ·
What is the best and fastest way to find a vacuum leak on my 1996 impala. It idles at 950 rpm. Rpm jumps around when i shift to drive. Change alot of parts and still no luck. Could it be the brake booster when i press the brake pedal? Oh yeah, when i cut A/c on the idle stick at 1200 rpm then settles at 1000 rpm.
 
#2 ·
Imho, an unlit propane torch works good for finding vacuum leaks. If you dont find anything with the torch, and you suspect the brake booster, try unplugging the vacuum hose going to it and plugging the hose with something. Crank the car, and see if it still idles funny, but beware as mashing the brake pedal will be a pita while the booster is unhooked.
 
#4 ·
Here are a couple common vaccum leak areas to look for.
1) The rubber portion of the PCV hose that attaches to the from of the intake under the throttle body.
2) The OTHER rubber end of the PCV tube where it attaches to the PCV valve on the driver's side of the intake manifold. When this one goes, it is usually on the bottom and you cannot see it until removing the line.

See attached pics. Good luck!
 

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#5 ·
Always a huge potential of leak(s) at the front and rear china walls! The OEM sealant just shrivvels up and disappears after a decade or so. ;)
 
#6 ·
Always a huge potential of leak(s) at the front and rear china walls! The OEM sealant just shrivvels up and disappears after a decade or so. ;)
^^^^ He means between the intake and the block. ;)
 
#9 · (Edited)
Correctomundo.

Ssssooooooo, weekend's almost over. You pop that intake yet? ::Wink::
 

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#7 ·
I use water with a couple of drops of dishwashing liquid. Spray it on the vacuum lines, and it will suck it up if there is a leak. The dishwashing liquid is to break the surface tension of the water. It is a lot safer than propane floating around the engine compartment.
 
#10 ·
engine rebuilt last summer

I had my engine rebuilt and weaker than before. the mechanic says its running lean on the dyno 13.5-15 WOT. I had my pcm programmed by Bryan Herter before and checked afterwards. Bryan says it a vacuum leak. I looked all over this engine and cant find nothing yet.I did not get a chance to try any of your response yet.I'm waiting on my service manual to come this week.
 
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