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Car dies when I touch brakes


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Tilrak
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Jan 14, 2009, 10:52 PM

Post #1 of 4 (624 views)
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Car dies when I touch brakes Sign In

I drive a 98 Pontiac Bonneville, 3.7 I think, with 180k miles. My check engine light came on, and when the codes were read, it said there was a problem with the Mass Air Sensor or the Map sensor. Sometimes when it changes gears, it rides rough, and sometimes when I touch the brakes, the car will drop dramatically in RPM's, and even die....frequently. I've taken it to a repair shop, and he tried cleaning the Mass Air Flow Sensor, changed the PCV pipe or valve, and still no change. He thinks it might be the Crank Sensor, but can't get it to fail. Any suggestions? Thanks Josh


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jan 15, 2009, 6:52 AM

Post #2 of 4 (621 views)
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Re: Car dies when I touch brakes [In reply to] Sign In

With it this sensitive to using the brakes I'd be checking for a power booster leak,

T
_________________________________________
Long retired now


Loren Champlain Sr
Veteran / Moderator
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Jan 15, 2009, 7:09 PM

Post #3 of 4 (612 views)
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Re: Car dies when I touch brakes [In reply to] Sign In

Have you had the codes pulled since the MAF sensor was cleaned? If the MAF code comes back, it's probably the problem. The MAF sensor reads the temperature and volume of air flowing past it, relays that information to the PCM and delivers fuel accordingly. For some reason, don't see a lot of contaminated MAF sensors of GMs. Fords, yes. The MAP sensor detects engine vacuum. If it 'sees' a drop in manifold vacuum, the PCM assumes that you are under load, and dumps fuel. MAP sensors can't be cleaned. So, to add to Tom's suggestion, if you have a brake booster or anything else that is leaking vacuum, that can cause the MAP sensor to get faulty information. It doesn't always work, but you can take a scewdriver handle and gently tap on the MAF sensor. If the engine stumbles, it's definitely a faulty MAF. As I said, it doesn't always work. The crank sensor is a common failure on GMs, but usually, not an intermittent problem. If it goes south, the engine will not run. And, very seldom will set a DTC.
Loren
SW Washington


Jeff Norfolk
Enthusiast
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Jan 15, 2009, 9:20 PM

Post #4 of 4 (607 views)
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Re: Car dies when I touch brakes [In reply to] Sign In

Have the shop check the pins on the MAF plug. Most people will unplug the MAF to check the air filter and over time the plug becomes loose. Start the car and then wiggle the plug a bit. See if you can duplicate the symptoms.
Jeff




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