Help with 90' 200TQA ...lite throttle surging

[Nicholas Lawrence]

    Car is 1990 200TQA.  At very light throttle the car surges, (feels like
either partial or full shut off), sometimes enough to spill coffee and at
least its uncomfortable and probably hard on drive line.
    Can happen at any speed and any rpm.  Going down slight grade on freeway
where little throttle is required, going 25 -35 mph, slowing for stop signs.
    Things I or others have done  that might be related. No Impact.
        Ignition wires, cap, rotor and plugs
        multi-temp switch,     throttle switch,      oxygen sensor
        valve cover T-hose,      intercooler MM hose,
    I have measured fuel pressure
    I had a shop measure fuel pressure and adjust mixture.
    Searched for vacuum leaks (but only at idle?)  with stethoscope,
    engine runs rough or stalls with dip-stick pulled.
    I blocked off vacuum brake booster (yes I do have vac brakes)
    Other related mods...C Smith spring,  by-pass valve

    It seems a couple of years ago this specific topic was discussed but I
don't remember if anyone found a cure.

    TIA ,    looking for more help and suggestions on what to check.

    Nick
    '90 200TQA
    '90 100
    '91 100
        gone from fleet ...'90 100 5spd, '85 5k, '85 5k wgn 5spd