Hey everyone,
I'm a new user but have been coming here for about a year for resources.
I have a 94 SC400 which i acquired late last year and very recently the engine has been running so badly it can't be driven.

I started it earlier and it barely holds an idle and wants to stall if the slightest throttle is given. I suspected a vacuum leak but only found one of the manifold bolts were the slightest tad loose. Started it again and everything seemed fine. Reinstalled the intake and it runs like garbage again.

Important note: I've been using this car with the MAF disconnected as it causes the engine to run eye-watering rich.
If I plug the MAF in, the cruddy idle goes away and i can rev the engine, but it renders the sane effect. As such I don't think it's a fuel problem.
With the intake removed, covering either the throttle body or IACV port cures the idle, but if you were to cover the throttle body ONLY and open the throttle will the engine rev. Covering both causes the engine to stall—so i don't suspect a vacuum leak.

Work i've done up to this point: replaced knock sensors and lead wires, tested and calibrated throttle sensor, cleaned IACV and EGR, cleaned manifold plenum and runners, throttle body and replaced intake gaskets. Plugs and wires seem ok.

Power steering pump is bypassed, power steering idle booster is deleted for the time being. I cleaned the alternator yesterday because i was noticing a high load on the electrical system (fans slowing with brake lights on etc).
Immediately afterwards the car seemed just fine.

The idle always eventually becomes a little lumpy but I accept this as fair trade because i do not daily drive this car. I have CEL codes 24, 27 and 31.

Appreciate any advice, thank you!