Just a quick heads up for you guys. My short term fuel trims on both banks suddenly pegged out lean at idle and it threw a check engine light. Some times it would go into open loop fault before hitting closed loop.

Looked at the graphs of the MAF and O2 sensor outputs and they were fine. Fuel pressure was at 50psi, so it was not that either (just to be sure on these BTW).

The STFT dropped at 2500rpm, so it was a vacuum leak. Although I smoked the engine, it did not show any smoke coming from the dipstick tube where it meets the block. I only found it when I checked the o rings on the top of the dipstick and could hear a noise from the tube. The o ring was shot, and I replaced it - total fuel trims are now +/- 3%

As I say, just a heads up, as I could not see smoke, so thought I would share this