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Old 08-31-2021, 07:12 PM   #1
sebastian323
Scooby Newbie
 
Member#: 510671
Join Date: Jan 2020
Chapter/Region: SCIC
Location: California
Vehicle:
2006 WRX
Gray

Default Possible to have vacuum leak when fuel trims are consitely negative ?

Hello,


My car refuses to function properly once the MAF sensor is plugged in. The idle is smooth but begins to hunt as soon as I tap the gas pedal in neutral Additionally, as soon as I put the car into neutral after driving fairly hard, the engine stalls. The fuel trims are consistently negative with the MAF plugged in or not. The trims are on the order of up to -20% combined AFR learning and correction.



I bought the car used without an engine and have never seen it running well. As soon as I remove the MAF sensor, the car goes into limp mode, where the operation is based off the MAP sensor pressure reading. The idle no longer hunts when I tap the gas in neutral and the car begins to operate more or less normally. I will also add that I am on the stock airbox. The car manages to "stabilize" the AFR to 14.7 in closed loop on both the wideband and stock sensor, though both could be reading wrong due to an exhaust leak.



Is it possible I have some overlooked vacuum leak ? (i smoke tested it and patched a few very minor leaks) . Maybe an exhaust leak ? I will also be checking continuity on every pin in the sensor. The voltage does change with load on the MAF however.
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Old 08-31-2021, 07:16 PM   #2
xtremewlr
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Member#: 525652
Join Date: Jul 2021
Chapter/Region: SWIC
Location: Tucson, AZ
Vehicle:
2006 STI
WR Blue

Default

Just a random thought, but do you have the MAF facing the correct direction?

I did that on mine once and put the MAF in facing the wrong direction and it ran like crap until I reversed it from what I thought was correct.
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