Thanks for the thoughts - that's a good idea, I'll check for leaks this weekend. It seems counter-intuitive though, wouldn't a leak somewhere on the intake side of an engine result in MORE air coming into the cylinder (because the intake is at vacuum), thus causing a lean condition?

My AFRs now go to 13.9 while cruising on the freeway, after slowly falling from 14.7. I release the throttle briefly, AFRs go back to 14.7 and slowly drop to 13.9 and hold. The e-manage has been completely disconnected, there are no extra electronics affecting the sensors, injectors, ignition, or anything.

Long term fuel trims are at -22 to -25 (max) right now while it happens, while short term trims are at 0. This is unusual for my car, both LTFT and STFT typically always remained within +/- 5. My fuel setup is unchanged - I still have 440 injectors running at an idle pressure of 18 psi, or 20 psi at cruise.

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO