Rich Condition (Negative Fuel Trims)

1996 V6...Still trying to figure out why my truck fuel trims are negative at idle (-15) and seem to go close to 0 under load. My Maf is reading 3.8-4.2 g/s. TPS reads 3.5% at Idle and 65% at WOT. O2 Bank 1 sensors seem to be between .03V and .9V. O2 bank 2 seems to be running smoothly. Timing Advance around 20 at idle and 5 at WOT. I dont know what timing advance does or if these are good numbers. Engine RPM is 625 at Idle.

Any help would be appreciated. Don't wanna throw the parts cannon at it. Fuel Pressure regulator? Leaking/ Wrong Fuel Injectors? OverReporting Maf? Anything else?

Edit: Engine was rebuilt 10,000 miles ago, but I do not know when the rich condition started because I didn't have a code reader. Also Fuel Injectors were replaced around that time.

Recently replaced Front Main Seal. aligned timing marks, if i was off a tooth what would happen?

 

Everything sounds fine aside from the fuel trim. Do you have a Check Engine Light?

 

no check engine light

 

Suppose it could be injectors then. Idk if I'd worry about it too much if it's just when idling and you don't have any bad symptoms

 

seems like FSM wants Idle rpm to be around 750. Would I just adjust throttle cable?

 

No, there's a screw on the throttle body