I have a 1992 4.3W CPMFI that is very hard to start cold and stumbles badly when throttle is opened. Fuel pressure check gives 60 PSI before engine starts, 54 PSI at idle or running, jump to 60+ when throttle opened. I replaced the "Spider" injector/regulator assemble to no avail. When finally running is smooth at steady state. Cold start reaction: fires, runs rough for a few seconds, dies. Eventually runs longer and longer till it keeps running and smooths out.
This engine is a transplant in a non GM vehicle so all non essential wiring is not hooked up, no dash.
The engine sat for about 6 years with ethanol fuel in it so first had to replace fuel filter and clean tank, pump seems to be OK, a bit noisy.
Any ideas? I'm pulling what little hair I have left out.