it's an 86 5ktqa

Recently put in the qlcc which made no difference to this pre-exisiting condition. (I had high hopes)
Car is otherwise stock "except" for the turbo and downpipe, cat removed and the aforementioned qlcc. Had turbo rebuilt with a slightly larger wheel apprx. 10%.

On light, partial throttle all is well, mat it and it stumbles.

Did all the normal vacuum leak checks, pull the dipstick: cough, sputter. Pull the oil cap, she'll die. Checked and rechecked the hoses both visually and by tempting fate with a few shots of brake cleaner.

MFTS is new, head was rebuilt last year, timing is spot on.

Replaced the throttle position sensor and threw in new plugs this afternoon, still stumbles. Old plugs were evenly kinda grey-ish on the electrode.

I'm reading 1.3 bar or 6 to 7lbs max boost, want to up things a bit but not before I figure this out.

Fuel pump is not the quietest so that's next on the hit list with a replacement filter seeing as the old one is coming on up to it's second year.

What are the symptoms of a dying fuel pressure regulator? Or is this a blatant case of weak fuel pump ready to tank?

TIA folks!

When it stumbles, does it last for long as long as your foot is down, or is it just a cough or hiccup that goes away and the power returns? Do you happen to see black exhaust smoke when you mash the pedal down at the same time it's stumbling? If you do, it might be rich at that point, which would mean that not all the air that's sucked in is being delivered to the engine, which means boost air is escaping somwhere before the intake (MM hose)causing a rich condition.
If you think it's lean, could your idle mixture screw (rising air plate adjustment)have been tampered, or adjusted too lean for a previous condition. If it's adjusted lean at idle, the whole range of power will be lean too. A CO check is in order.
Check it out

no black smoke, at least none that I can see while driving, idle mixture no idea. good call though, thanks!

OK!!!!
Did you ever replace the O2 sensor???

Meaning my QLCC is fried...sh*t!! It's intermittent so hopefully its just a bad solder joint.