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I just installed a new intake gasket and plenum. I start the…

Customer Question
I just installed a...

I just installed a new intake gasket and plenum. I start the car and it wants to shut off. If i am driving it and let off the gas it will stall

Mechanic's Assistant: Is this your first time dealing with this issue? What size is your engine?

Yes, 3.8

Mechanic's Assistant: What is the model/year of your Pontiac?

2007 base model

Mechanic's Assistant: Are you fixing your vehicle yourself? What have you tried so far?

Yes, nothing Im not sure what to try. maybe the mass air flow sensor? its ran rough for awhile before I replace the intake gasket, but never shut off on me

Submitted: 11 months ago.Category: Pontiac
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Answered in 1 day by:
9/10/2017
Pontiac Mechanic: Matt, Engineer replied 11 months ago
Matt
Matt, Engineer
Category: Pontiac
Satisfied Customers: 23,474
Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
Verified

Hello
This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion ill make a leak worse) so leaks can be better or worse as the engine heats up.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth cleaning out the throttle body as these get clogged up with carbon and some brake cleaner washed through helps free things off.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

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Pontiac Mechanic: Matt, Engineer replied 11 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

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Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.

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