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Car spontaneously running rich

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So, I just finished putting my car back together, after firing it up I noticed that the car was running extremely rich at idle and partial throttle... I had to pull over 20% of fuel at idle to get the car to approach stoich levels (11.7 AFR running ethanol/E54).

I had something similar happen to me a few years ago, it turned out to be a vacuum leak, or at least I think so...

Any ideas as to what could be causing this?

I'm using a ProEFI 48 box on turbo VQ35DE (InfinitI G35 coupe)


If it's not a vacuum leak, then could it be fuel pressure, sticky/leaking injector or cam timing (did you connect the control solenoids)? What have you changed or been working on?

I'd confirm that all of the inputs to the ECU are reading correctly. I'd be suspicious of inputs that affect the load input to the ECU such as MAP, however anything that affects a compensation to the fuel delivery could also be an issue - TPS, IAT, ECT for example.

I'd retrace your steps and check into everything you've changed since the last time the engine was running correctly.