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Old 05-31-2019, 06:29 PM   #1
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Default 08 Chevy Malibu - Dies when trying to idle, runs fine at higher revs

Hey guys,

Friend has a 2008 Chevy Malibu that started acting up on her. 160k.

It starts, but idles rough and eventually starves itself and dies within a minute or 2. But initial idle for 5-10 secs is smooth.

If I rev it over 2500 rpm and keep it up, it keeps running and drives fine. No misfires.

No check engine lights. Nothing on the scanner. Resat the fuel pump relay and checked fuses. Resat MAF connector.

I think it's her fuel pump going out. Any other thoughts on what it could be??

Thanks
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Old 05-31-2019, 07:20 PM   #2
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i would think a bad fuel pump would make things worse at higher rpm.
2.4 I4 i assume? what do the fuel trims look like? sounds like a vacuum leak
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Old 05-31-2019, 07:27 PM   #3
 
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Unplug the MAF and see what happens
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Old 05-31-2019, 07:46 PM   #4
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Originally Posted by bikrboy128 View Post
i would think a bad fuel pump would make things worse at higher rpm.
2.4 I4 i assume? what do the fuel trims look like? sounds like a vacuum leak
Yep 2.4l

How do you check fuel trims?
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Old 05-31-2019, 07:46 PM   #5
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Unplug the MAF and see what happens
Will give that a shot
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Old 05-31-2019, 07:55 PM   #6
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i would think a bad fuel pump would make things worse at higher rpm.
2.4 I4 i assume? what do the fuel trims look like? sounds like a vacuum leak
Yeah that's true about the fuel pump . My thoughts was if the revs are higher, it's pulling more fuel and stays running but when pressure drops for idle, it then starves from the lower pressure not sending enough fuel.

But that is probably not how it works now that I think of it more.

Vacuum leak it could be. I didn't get to take it apart yet, just side of the road diagnosis and then I drove it to her place about 2 miles just keeping the revs up
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Old 05-31-2019, 08:48 PM   #7
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can the scan tool you have do live data? check STFT and LTFT. they should be close to 0
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Old 05-31-2019, 08:59 PM   #8
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can the scan tool you have do live data? check STFT and LTFT. they should be close to 0
No my regular scan tool didn't look like it did (or maybe I don't know how to use it lmao) but my Bluetooth odb2 might, I just didn't have it with me.

I'll be stopping by tomorrow to take another look at it when I have some tools
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Old 06-01-2019, 01:55 PM   #9
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Unplug the MAF and see what happens
So... Unplugged the MAF, car dies almost right away when trying to start. Plugged it back in...and now it is idling fine

Did the same thing yesterday except didn't try to start it with it unplugged and that didn't do anything.
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can the scan tool you have do live data? check STFT and LTFT. they should be close to 0
Here's the readout from my Bluetooth ODB when idling

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Old 06-01-2019, 01:55 PM   #10
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Gonna take it for a ride, but it seems to have fixed itself
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Old 06-01-2019, 02:00 PM   #11
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those fuel trims are super lean. you likely have a vacuum leak somewhere or the MAF is toast. 0% on both STFT and LTFT is ideal, +/- 10% is acceptable.
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Old 06-01-2019, 02:15 PM   #12
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those fuel trims are super lean. you likely have a vacuum leak somewhere or the MAF is toast. 0% on both STFT and LTFT is ideal, +/- 10% is acceptable.
Yeah it just threw a P0171 code for system bank 1 lean but now it is idling so the computer figured it out.
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Old 06-01-2019, 02:20 PM   #13
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those fuel trims are super lean. you likely have a vacuum leak somewhere or the MAF is toast. 0% on both STFT and LTFT is ideal, +/- 10% is acceptable.
It's bouncing at idle under 5% each way now after going for a 5-10 min drive

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Old 06-01-2019, 02:24 PM   #14
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Oh but that's just for stft
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Old 06-01-2019, 03:34 PM   #15
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Took apart MAF and cleaned it, took apart throttle body. Check all hoses.

I think I found the issue... Rubber gasket between throttle body and intake is ripped. After cleaning and putting everything back together, much better trims now. Pretty sure that gasket and the dirty MAF might be the problem



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Old 06-01-2019, 03:54 PM   #16
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Anyone know what that gasket would be called?

Throttle body gasket is giving me the inner green one not the outer
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Old 06-01-2019, 11:10 PM   #17
 
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Quote:
Originally Posted by tinfoilhat View Post
So... Unplugged the MAF, car dies almost right away when trying to start. Plugged it back in...and now it is idling fine

Did the same thing yesterday except didn't try to start it with it unplugged and that didn't do anything.Here's the readout from my Bluetooth ODB when idling

Attachment 40254
Once the car is warmed up and idling , then unplug it. If it corrects the stalling, your MAF is bad. During cold start the computer relies on the O2 sensor only. It could also have an intermittent short. Tap test it by using a tap with the big end of a screwdriver. If it stalls/stumbles itís got an issue.
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Old 06-01-2019, 11:15 PM   #18
 
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I read a little further down and see you found the issue. After you replace the coupler that is cracked you may also want to replace the injector o rings that seal to the engine side. They tend to shrink over time and leak
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