I have a 2001 Toyota Corolla.

Lately it has been throwing the P0171 code (system too lean). My short term fuel trim is normal at idle. +/- 5 % at idle and long term fuel trim is high at idle +18 %.

When I rev the engine to 1500 rpm the short term stays the same and long term fuel trim goes down to about 14%. Weird thing is when I drive the car, the short term fuel trim is normal and the long term goes down to 7 percent or so, BUT intermittently at around 2200 to 2500 rpm the short term shoots up to around 25 percent and long term fuel trim goes to 35 %. This is the point where I throw the P0171 code.

Any help would be appreciated.

  • Welcome to Motor Vehicle Maintenance & Repair! Oct 23, 2018 at 0:40
  • I'm not sure, but I'd start with vacuum leaks - especially inspect the intake hose(s) and look for cracks. This could be a "false air" or "unmetered air" issue.
    – SteveRacer
    Oct 23, 2018 at 7:24
  • Jake, are you accelerating when the STFT spikes?
    – Zaid
    Oct 23, 2018 at 7:28
  • Thank you, SteveRacer, this is what i was thinking also. And Zaid, yes i believe i was accelerating when the stft spikes. I would have to check. It only does this once every few miles though. And the engine load was 35 percent when my computer threw the code Oct 23, 2018 at 17:45


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