Hey Scotty, I’ve got a 4cyl 1987 Pontiac Fiero with 156,000 miles on the clock. Ever since I bought it it’s had issues with hesitation, bucking, missing at idle, and missing under heavy load unless the rpms are above 3,000. When the engine is under operating temperature it just doesn’t seem to want to run correctly and often will throw a lean code. I’ve switched out every single sensor in the car, spark plugs, coil packs, ignition control module, fuel injector (TBI) and wires to no avail. The only telling part is that it runs much better in the winter than in the summer, however, it runs particularly bad after it rains or is extremely humid outside. Often, if I go to the store on a hot day when I get back in the car after shopping it won’t start up. Any ideas or is it time to take it to a GM dealership? I’ve tried to find a vacuum leak by spraying down the intake with carb cleaner but it doesn’t change how it runs.
The problems you're talking about could have a number of causes, but it sounds like you've checked all the obvious ones.
I would caution you to not take this to any old GM dealer - your car is 34 years old, so there's probably nobody there who has ever worked on a Fiero.
I'd suggest you start cruising the Fiero-specific forums to find advice and/or a Fiero- knowledgeable mechanic - there are several here: https://www.google.com/search?client=firefox-b-1-d&q=fiero+forum
It's probably worth doing compression and leakdown tests to make verify that the engine is in good condition internally.
