Possible MAFS issues or detonation sensor

[PapaSmurf2k3]

Yeah a leak after the MAF can cause rich conditions in a turbo car (you are essentially leaking metered air), but in non-turbo, you are sucking in non-metered air, so it should lean it out.

I've actually done that just to get engines to run with larger injectors. Induce a few vacuum leaks in the intake manifold, or hack the MAF (if its before the turbo) by allowing the turbo to suck in unmetered air (either drill a hole in the tube or something, or just crack the MAF off the coupler a bit).