1992 pontiac sunbird se, convertible, vin ig2jb34t1n7589065.
the car developed a miss. I ran fuel injector cleaner thru the tank. Miss went away. A month later it came back.
i took it to the local mechanic.
they found a bad plug wire, and two bad plugs.
put in a new ecm, no change.
where the wiring harness goes thru the firewall, they found 2 or 3 chewed wires.
the shop diagnostic tool showed rpm's decreasing as fuel was added.
i went to a local scrap yard and brought them a wiring harness, wrong one! Turns out that that year had like sixteen differant ones.
mechanic repaired the chewed wires with bullet splices.
rpm's on the diagnostic tool now operate normally.
still missing and huge gas smell.
diagnostic tool has always showed no codes!