Hummer H3 For the Hummer driver who wants the rugged look and off road capabilities of the Hummer, but in a smaller size and with a more fuel economy friendly engine.

Need help with rough idle

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Old Mar 5, 2026 | 04:54 PM
  #11  
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Originally Posted by MadDogBimmer89
EVAP purge valve possibly? Do you have a scanner that you can connect to and check live data?

Reason I say EVAP purge valve, I read they can become stuck open and essentially flood the engine with fuel vapor, car will run rough/rich until it clears out and then will be smooth again. Live data will show more than normal negative fuel trims during this time.
yes I have autel scanned I’ll see if I can figure out how to test the evap
 
Old Mar 5, 2026 | 06:35 PM
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Originally Posted by NFS
I can check , where on the fuel rail you check for pressure ? Is it that green cap?
 
Old Mar 6, 2026 | 10:44 AM
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Originally Posted by NFS
yes I have autel scanned I’ll see if I can figure out how to test the evap
With a bidirectional scanner there's an option to open and close purge valve 0-100% watch your trims as you open it. If the purge valve is functioning as it should you'll see trims go negative as the engine trying to reduce fuel since it's sensing rich mixture. Or just watch your trims when the truck is running rough, that could be a good clue to rule out common possibilities.
 
Old Mar 8, 2026 | 09:47 AM
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I checked fuel pressure at crank I am getting 60 and at idle is 60 and when it was running little rough it stayed at 60
 
Old Mar 8, 2026 | 03:58 PM
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Originally Posted by NFS
I checked fuel pressure at crank I am getting 60 and at idle is 60 and when it was running little rough it stayed at 60
You got fuel.
Now check air.
Test the MAF sensor>>> Unplugging Method (Quick Test): With the engine running, disconnect the electrical connector from the MAF sensor. If the engine stalls or changes idle significantly, the sensor is likely working. If there is no change in behavior, it is likely bad.
 
Old Mar 8, 2026 | 04:04 PM
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Originally Posted by hummerz
You got fuel.
Now check air.
Test the MAF sensor>>> Unplugging Method (Quick Test): With the engine running, disconnect the electrical connector from the MAF sensor. If the engine stalls or changes idle significantly, the sensor is likely working. If there is no change in behavior, it is likely bad.

I did that was one of the tests that I did and I also installed a new maf . It’s working properly
 
Old Mar 8, 2026 | 04:30 PM
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STOCK CAI?
Another quick check >>>with a scanner connected look at ECT after startup.
 
Old Mar 8, 2026 | 05:53 PM
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Originally Posted by hummerz
STOCK CAI?
Another quick check >>>with a scanner connected look at ECT after startup.
no I have aftermarket intake . But didn’t have a problem before with it. I Also did a smoke vacuum test to see if there is any leak and there was none . I have new Tempreture sensor installed also because I thought that may be bad but it wasn’t
 
Old Mar 8, 2026 | 06:11 PM
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Originally Posted by NFS
no I have aftermarket intake . But didn’t have a problem before with it. I Also did a smoke vacuum test to see if there is any leak and there was none . I have new Tempreture sensor installed also because I thought that may be bad but it wasn’t
AM intake=red flag! Answer previous question>>>What temp does your scanner show at startup?
 
Old Mar 8, 2026 | 07:03 PM
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Originally Posted by hummerz
AM intake=red flag! Answer previous question>>>What temp does your scanner show at startup?
oh come on I had that Intake for years and no problem, when I checked now the temp at startup it was 80F
 



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