1993 buick riviera hard to start and won't stay running

Did you check your fuel pressure it should be about 55 to 60 psi

Check your fuel pressure; if it is within specs, have a muffler shop test your back-pressure from your catalytic converter. There are other things that can cause strange problems like this but it is a process of elimination.

how did you disconnect the battery, pos first then neg ? or neg first then pos ? try starting it and after started, hold your rpm at 1500, for about two minutes, then if still running, drive it to get to.speeds of 40 for about 15 minutes, this is to relearn if not, disconnect your battery, take the pos and neg cable and touch them together and hold for about a minute, then Connect them back, neg.first.then pos, then follow steps above to.relearn.

Yes it could be the things you mentioned, and also low fuel pressure.
Have you checked fuel pressure at the injectors with a gauge ?

Whether it is an electric problem, or gas problem

well this is a first but possible i suppose ?? the transponder has read the wrong chip and now it will not release the immobilisor ,so i think it may be a dealer job

unplug the cam sensor behind the water pump pulley; see if it starts; if it does, shut off engine; replace both cam and crank sensors because crank sensors go out in these engines

Dead battery and bad gas,should start but will have bad gas smell, after you got it running add gas and fuel additive, change all fluid, check belt's and hoses. also have brakes checked.Hope this was helpful.

Mine did the same thing, it apparently was the mass airflow sensor, however the computer module also had to be replaced. It runs fine now!!

Put fuel in it,then check the fuel pressure with a gauge. The tank unit maybe giving a false reading.