My 1984 fiero SE recently started acting weird. It has the 2.5l Iron Duke with a 5spd trans from an 87 gt. Most of the time it drives fine, but if i give it any more than 1/3 throttle, it was just shake and not accelerate very well. My fuel mileage also went from ~28mpg to ~24 mpg. The plugs, wires, and cap and rotor were all replaced in april, but I put a new cap and rotor in since I was sure that was the problem. Nothing changed and now I'm stumped. Any help is appreciated

[This message has been edited by jhobbins (edited 12-24-2012).]

A fuel pressure check may be a good idea.

wouldn't a symptom of low fuel pressure be rough at low rpms and light throttle, but better at high rpms and more throttle?

I think it's the other way around. A car will idle on low fuel pressure, but when you ask it to deliver more speed, the fuel delivery does not keep up.

okay thanks I didn't know that. So im probably looking at fuel filter or possibly pump if it comes up low?

yup.....

the other possibility may be a partially blocked fuel injector..(if the fuel pressure checks out)

My Duke did the same thing, fuel pump only had 6 psi, enough to run at idle and part throttle but it would stumble badly at WOT. It was the original pump, lasted 24 years. The worst part with dukes is that you have to make a tee adapter on the supply line to measure fuel pressure, there is no Schrader type fitting.