I have a 1988 GMC S15 in my shop and it will flood without cranking, only goes 30 mph, fouls spark plugs, and its hard to start hot or cold. We put brand new distributor caps, spark plugs, wires, rotor button, tried a different map sensor, removed the catalytic converter, did a compression test all cylinders were 100 lbs.
If this is a 2.5 and I think it is, they had a problem with the reluctor in the dist cracking. The distributor has to be replaced to fix this. As the TBI picks up pulses from the distributor to put fuel in this may be your problem. I've had the same problem with a V8 though with the same problem. I've been unable to find anything or diagnose what's wrong with it. Multiple items have been replaced and still the same problem. With yours that is the only thing I can think of unless your fuel pressure is to high. A TBI unit should only have 9-11 p.S.I.