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Problem: Weak acceleration, light rough idle, occasionally have to press down excessively hard on the gas to get a solid response and pick up speed (i.e. when merging onto a highway). It feels like a delayed response to my foot on the pedal.
No codes, never had a check engine light.. zero misfires, new OEM coils and plugs were put in 15k miles ago (this problem has lasted since before then).
I downloaded TouchScan on my laptop (was using Torque on my phone but it's limited) and was checking my fuel trims to try and figure out what's up..
My LTFT has typically lingered between 5.5 - 7.5%. Today when monitoring STFT and RPMs, I noticed when I held my RPMs at 2,500 the STFT would increase and remain higher until I let off the RPMs, then STFT dropped to zero. When on the highway my STFT goes up to +12-15% while I am accelerating at ~4k rpms, then drops as the RPMs drop.
MAF is completely clean, checked it out and sprayed MAF cleaner regardless. New air filter as well. No change.
Re: STFT increases with RPMs, fuel delivery issue?
STFT should be close to zero except for transient events (mashing the throttle or sudden liftoff). STFT values that are positive or negative will affect the LTFT values, until the STFT reaches zero. The point of these PID's is to prove the computer can control the fuel introduced into the engine. Transient fuel events are not computed into long term fuel trims because it is transient, meaning above (or below) the norm. Doing so negates the entire fuel control strategy.
For example, if your LTFT is 8% and your STFT is 3%, in an ideal situation, the PCM will learn the new constant STFT value, and add it to the LTFT, resulting in a LTFT of 11%, and a STFT of 0%. This indicates complete fuel control (albeit in some systems, slightly too rich). The goal is to compensate as much as possible, and get the short term fuel trims to 0%, demonstrating fuel control.
When did this start? Have you contacted the dealer regarding this issue? 165K is a lot for a 2012, was this a previous rental vehicle?
STFT increases with RPMs, fuel delivery issue?
