My 2005 Gen 2 Prius has developed an strange intermittent issue over the past month (reproduced only once so far). While driving under load (especially climbing long grades), the engine suddenly misfires badly for a few seconds. It then either continues running "normally" with very low power or triggers P0A0F, forcing me to coast and power cycle the car. First occurrence: ~1 month ago on an interstate onramp; had to coast off with P0A0F. Unfortunately I just had to reset it on the side of the road to make it home and didn't think to screenshot the codes or save the freezeframe data. Second: Today, after ~1000 miles of normal driving since the first. Engine returned to running normally after ~5 seconds, and I was able to make it home, albeit on noticeably reduced power. Techstream scan today shows: P0171 (System Too Lean Bank 1) P0442 P0446 Live data at idle @~155F (heater on to force engine run)and partial throttle ~1600rpm shows: B1S1 STFT ≈ -21%, LTFT +44.5%. The lean code combined with the evap codes makes me think perhaps a cracked evap line and faulty valve? As I've only had it happen twice within the past month/1k miles, I find it difficult to believe a leaking gas cap would be the source of that issue. Not sure what to make of the fuel trims either in this case, but fuel economy is noticeably down over the past 1k miles since the issue first happened. Any ideas on where I should start looking? I'll clean the MAF tomorrow as a sanity check, but it seems very odd that it'd be intermittent like this.
