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Old 02-15-2021, 06:09 PM   #1
mitchfishman5
Scooby Newbie
 
Member#: 510946
Join Date: Jan 2020
Chapter/Region: MWSOC
Location: Northville, MI
Vehicle:
2004 WRX
World Rally Blue

Default Suddenly Running Super Lean at Idle

Hey guys, I just started cleaning up and repairing my new to me 04 WRX. After a boost leak test, I ended up replacing a bunch of hoses, my turbo inlet with an aftermarket Mishimoto, my intercooler hoses, BOV return hose, and I got a good deal on a Grimmspeed EBCS so I threw that in as well. So with the changes and the catless downpipe the previous owner had added, I began my E-Tune process.

I received a base map and because of the circumstances was forced to take it on a 60-mile work trip. All was fine before the trip except for a little bit of a rough idle and while I was driving but when I pulled off the freeway the engine began running lean at idle (AFR of about 16-17 ) and threw a P0171. I parked it and tried again in the morning with even worse results (AFR running in the low 20's!). My buddy suggested I clean the IACV and that it may have been responsible for the weird idle prior and lean mix now. I cleaned it out and replaced the gasket and my problem was seemingly solved.

This morning when I turned it on I got a high idle at 2500 where the car was running about 14.7 but when the idle would drop down to 800 it would run super lean again (20's) before bouncing back up. I'm not sure what it does at cruising speeds because I am afraid of damaging the engine. Now, this afternoon, my tuner looked at my logs before my trip and told me it looks like I have a vacuum leak because my fuel trims are high at idle and my airflow is lower than it should be. I honestly have no idea what's going on here. I plan on having a leak test done but this seems like a bigger problem than just a small boost leak. What do you guys think is happening?
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Last edited by mitchfishman5; 02-15-2021 at 06:18 PM. Reason: Readabilty
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Old 02-15-2021, 06:47 PM   #2
TwistedAxles101
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Member#: 379235
Join Date: Jan 2014
Chapter/Region: MAIC
Location: Waynesboro VA
Vehicle:
2002 Impreza WRX
Blaze Yellow

Default

It definitely sounds like you have a vacuum leak, especially with your high idle. You mentioned installing a turbo inlet, you may have broken a vacuum hose. Go back and check for broken and cracked hoses. It's also a good idea to go back and make sure all of your clamps are properly installed and tightened. You could also take some brake cleaner and spray around suspect area, your idle will raise when you spray the leak. Try the brake cleaner method at your own risk, it is flammable. There is a cluster of EVAP vacuum hoses right next to the turbo inlet hose behind your power steering pump.
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Old 02-15-2021, 06:58 PM   #3
mitchfishman5
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Member#: 510946
Join Date: Jan 2020
Chapter/Region: MWSOC
Location: Northville, MI
Vehicle:
2004 WRX
World Rally Blue

Default

Alright, that's very relieving to hear. I'll give it a shot tonight and see if it's anyplace obvious. Do you think I should worry about idling at such a lean AFR?
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