2ZR Turbo Yaris

[tmontague]

I would be very surprised if the vented valve cover has anything to do with your fuel trim issue as long as you have no open bungs on your intake or manifold down strem of the maf sensor. My concern with the vented valve cover was crankcase pressure issues as it normally has a vacuum on it pulling out the vapors. That said it shouldn't be a problem because any built up pressure will be greater than atmospheric pressures and vent out anyways.

The F/IC should be able to correct the fuel trims, but other than a vacuum leak I'm not sure why you are running lean fuel trims. FWIW ever since I went with an aftermarket full header back exhaust I have always run -12 to -14 LTFT. This was with my 1nz as well as the 2zr.

Check your oil catch can for vacuum leaks, happens a lot more than you would think and it was the source of a vacuum leak on my 1nz. Do your FT's change/normalize when you rev it to 3k rpm and hold it there? that is a good test of a vacuum leak as there is less vacuum on the system as the throttle opens.

I'll check my heater hoses tonight but the coolant should bleed itself out if that is infact the issue. Also it helps to have the front of the car jacked higher than the rear to aid in bleeding. It puts the rad cap at an even higher point than any other cooling system component to aid in air removal. Also coolant temps will rarely get up to full operating temp idling in a driveway so the heater core will still act as a heat sink even without the hvac fan running and it will still somewhat cool the coolant.

The downstream O2 sensor is a dumb sensor and shouldn't play a role in FT's unlike the upstream AFR sensor does. The downstream O2 sensor typically should throw a code P0420 etc when it is disconnected. But in my experience I have found this to be one of the last engine readiness checks that the ECU runs through so it may take some various condition driving for it to trigger on.

Good luck with the wiring!