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Old 05-31-2012, 08:15 PM   #1
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Hey guys when i start my car my boost is immediately at abt negative 3 and always idles at tht same level but when i get speed up and coast it goes down to neg. ten...whats causing this to happen..whats stopping my boost from full idle of neg. ten....how can i fix this...??
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Old 06-01-2012, 08:43 AM   #2
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There are two small devices that control boost ... the boost control solenoid and the boost control actuator. The boost control actuator has a small rod coming out of it that connects to a lever that controls a butterfly valve in the throttle body. With the engine off (no vacuum) the rod in the BCA should be fully extended. At idle (max vacuum), the rod in the BCA should be fully retracted. At WOT (min vacuum) it should be fully extended. Check to make sure this mechanism is moving freely. If it is binding it may not be fully retracting at idle which would result in boost when you don't want it. Also, check the vacuum line going to the BCA. If it has a leak the BCA won't receive fully vacuum at idle and may not fully retract.

Best way to check it is at idle disconnect and reconnect the vacuum line from the BCA a couple of times. When you disconnect the line the BCA rod should fully extend. When you reconnect it should fully retract.

You could have a damaged vacuum line, the butterfly mechanism could be binding, or the BCA could be defective. All easy fixes.
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Old 06-04-2012, 04:24 PM   #3
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Whn i disconnect the vacuum line it sputters and the level hovers at mid level...i wld guess this is a vacuum line issue...am i right or do u think different ...??
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Old 06-04-2012, 05:45 PM   #4
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Ok, lets clarify this. When your engine is idleing, what position is the arm in? Is it all the way up?
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Old 06-04-2012, 06:11 PM   #5
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Yes, I think you may have a vacuum leak.
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Old 06-04-2012, 11:02 PM   #6
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Its in the all correct positioning when running and off but when the car is running and i unplug the vacuum and plug it, it sputters like it wants to cut off and the levers staysu teetering at midlevel....
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Old 06-05-2012, 06:05 AM   #7
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Yes, it would appear you have a vacuum leak somewhere. With the engine running, check all of your vac lines by wiggling them and listen for any hissing or the engine run differently.
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Old 06-05-2012, 09:23 AM   #8
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Originally Posted by mello View Post
Its in the all correct positioning when running and off but when the car is running and i unplug the vacuum and plug it, it sputters like it wants to cut off and the levers staysu teetering at midlevel....
If you unplug the vacuum line from the BCA and the rod does not fully extend, you either have a bad BCA or the butterfly valve the rod actuates is not moving freely. Remove the BCA, disconnect the rod from the butterfly valve arm, and see if the butterfly valve arm moves freely, If not, spray WD-40 where the arm enters the throttle body, and on the back side of the throttle body where the arm exits. While rotating the arm keep spraying until the arm moves freely. Put it back together and see if it makes a difference. If not, you may have to replace the BCA.

I think you have vacuum problems, but if the BCA rod does not fully retract when you pull the vacuum hose off there is something else going on as well.

Where does the rod from the BCA sit when the engine is not running? Is it fully extended?
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