My LTFT are normally +/- 2%, STFT jump a little up and down, but not more than +/-5%.

From time to time, especially in hot days or after a spirited driving the LTFT make a jump to the negative side, especially the low load cells (0..11 and idle). They may go -7% or even lower. At the same time I see a richer AFR at WOT than usual.

After I turn off the engine, wait 5 min, the fuel trims go back to the old values.

How is this possible?


A couple of thoughts:

- No codes, no misfire, no overheating

- The Baro value goes up to 104 kPa after a WOT (clear why, does it matter?)

- After disconnecting/reconnecting the MAF or the IAT I notice something similar: does the PCM go in some kind of safe modus and injects more fuel?
If I had a bad IAT or MAF contact that would explain the negative trims. However: no IAT nor MAF codes.

- The original position of the IAT for my Vortech kit was after the air filter. Now it's just before the TB (I wanted to know the charge air temperature). The IAT can go pretty high (up to 170F, especially at idle in traffic, this because the bypass valve is recirculating the air).
Is that a reason for the PCM to mess with the fuel?

- the MAF is before the blower.


...any idea?

Thanks - Stefano