Intermittent vacum leak? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 01-23-2008, 12:49 AM   #1
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Default Intermittent vacum leak?

Hello all, im new to the forum but not new to whats going on under the hood. I drive a 99 Bonneville SE with the good ol' 3.8. the problem started this past summer when i accelerated rather hard and the car clunked, sputtered, almost stalled and really wrecked my day. the car began stalling when slowing down, and idling erratically. I stopped down to my local autozone - my preferred parts dealer and had them toss a scan tool on it. The scan came back MAF sensor. I remember reading about the computer using the MAP sensor for air intake calculations when the MAF sensor was not properly functioning or absent, so i disconnected the MAF sensor and after a hard start the problem was gone but i had a check engine light and reduced economy, a big issue with my change pile, er bank account. I replaced the bastard $150 sensor and the problem disappeared for about a week. the following week the car was stalling again so i again disconnected the sensor but noticed a very loud air rushing sound while under the hood coming from the airbox... not an essential part of the car properly running correct? i pressed on the airbox and wiggled it around and the noise went away... car ran fine for several days. then the noise came back, the car again had a very erratic idle but a couple secs on the throttle and its gone. the car will no longer run with the mass airflow sensor connected and i can hear this massive vacuum leak all the time and the car stalls at every stop or slow down unless i two-foot it. at a complete stop in park the idle will bounce from 500-1000 RPM for a few minutes then rev to 2000 or so RPM and return to a normal idle.... when the car is in low erratic idle mode the charge gauge reads right on the edge of the low red, 8 i believe? i cant remember off the top of my head. lights and fan dim drastically. Fuel millage is terrible, acceleration is pretty much the same, no oil or coolant consumption.

I have no idea what this could be. Any help at all would be awesome. Im totally stumped and its my primary driver, to my sub-par job, so i cant afford to take it to a shop.
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Old 01-23-2008, 10:13 AM   #2
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Welcome to the BC club, could you put the model yr. and trim level of your car in the sig. Thanks. From what I read maybe your accordion tube the connects the air box to the throttle body is loose. Have you checked all of your vacuum lines?
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Old 01-24-2008, 06:49 PM   #3
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You bet its a 99 SE. I've wiggled all the vacuum hoses and it doesn't trigger the issue... the car makes a very loud sound like its sucking a lot of air... i can hear it over the heater fan inside the car...
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Old 01-24-2008, 07:33 PM   #4
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Did you check all the rubber fittings on the vac lines also? Check your Evap canister and the vac lines going into it, which is located under the air filter box. Have your throttle body ever been removed? If that turns out ok It could be your EGR Valve
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Old 01-24-2008, 07:37 PM   #5
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Does it only do it on cold start?
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Old 01-24-2008, 11:48 PM   #6
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I'll scope out the canisters as soon as i can but it sounds too loud to be something small like a vacuum hose... has anyone else had this kind of problem?
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Old 01-25-2008, 02:58 PM   #7
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Hose to power brake booster or booster itself?
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Old 01-25-2008, 11:19 PM   #8
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I remember googling bonneville issues like this when it started and figured it was a common problem... it usually does it on a cold start and after a few minutes go away but will come back randomly when warm too... i scoped out the vacuum hoses under a bright shop light and saw no cracks.... the noise sounds closer to the engine than the brake boster
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Old 01-26-2008, 12:07 AM   #9
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Check the other end of the vacuum hose from the booster, also...where it connects to the fitting in the UIM, and check that fitting also. It clips into the UIM, and has an O-ring to help seal it.
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Old 01-27-2008, 02:08 PM   #10
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Default vacuum leak

Hi. I am having a similar problem with a possible vacuum leak and it is effecting my air conditioning. I only get a strong flow of air coming out of the upper defroster vents along the bottom edge of the windshield.

Just to help you out... I had to replace the 8 inch and the 5 inch long vacuum hoses that run from the intake manifold to the outer firewall ac box--which is just under that long fuse panel cover. It ends at a Y jack (vacuum) where it pokes out of the thick wire loom. This is all on the passenger'* side, just in front of that fuse block cover. It'* a little inboard from the hood spring assembly too. You cant miss it.

Those vacuum hoses were completely toasted on my car and I have 168,000 miles. I would recommend checking yours out too. Hope this helps you...

Let me know if you have any suggestions on my situation please.

Thanks
Todd
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