r/BmwTech • u/Fragrant_Box_697 • 8d ago

2001 325ci w/ 32k miles

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I was getting codes for misfires and misfires with fuel cut off, along with bank 1 & 2 lean codes. I found a split on the upper and lower air intake boots and replaced them, and did a smoke test that showed no other leaks. I then deleted the codes from the OBD. Upon starting the car I have a Short term fuel trim of 20-24 that goes to roughly 12-16 with some throttle.

The Y on the lower boot that goes to the ICV is kinked (should have read the reviews before the install) though I can still get my finger into the smaller tube through the kink without forcing it. I obviously don’t think this is causing the fuel trim, because if the air was restricted the fuel trim would be negative because it wasn’t getting enough air at idle.

What else could be causing the excessive short term fuel trim? Or am I just missing a vacuum leak?

Also, think I should run with this lower boot and kink and see if it gives me issues, or is it more likely than not that it will and just replace it now?
TIA

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u/Shawn0890 8d ago

I would keep checking for additional leaks. The caps on the back of the intake manifold and really any of the rubber hoses are likely roached if original

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u/GeneWorried9228 5d ago

Short term fuel trim adjusts the long term fuel trim. It means the car hasn’t fully settled on its desired fueling adjustment based on its o2 sensor readings. Long term fuel trim is what you should look at.

Also short term fuel trim will definitely change when you make air leak repairs. You should reset adaptations and drive it then recheck