RepairPal Certified shops can diagnose and repair your 1990 Buick Riviera. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
It's time for running some tests,
most likely fuel related, need to know fuel pressures, injector on times need to be measured.
Get it to someone with the proper tools.
runs fine once you get it started and it gets warmed up
all engines need additional fuel to operate when cold,(choke) once warm, it will run good with lean conditions.