Auto Parts: 1990 GMC S15 timing problem ?, gmc s15, sensor outputs

Question
I have a 90 GMC S15 with a 2.5 l4 motor and standard trans. After taking it to 2 shops it runs worse than it did before. it won't start easily , stumbles on acceleration , idles either too high or too low ,basically runs like _____. The computer has been replaced ,also the distributor . Do you have any idea what is wrong? Thank you

Answer
I hope your "mechanic" didn't run straight to the PCM to replace it.  There are many things that can be checked before the PCM needs to be changed.  That should be your LAST resort any time.  Check all your sensor outputs first, then fuel filter, fuel pressure, and fuel injectors.