It seems on Ebay there are a few sellers selling a "Timing Advance Kit" for Fiero's (and other vehicle's) and claiming 20+hp gains. The kit is a $0.37 resistor you add to the MAT sensor (located on the air filter assembly) on a Fiero; in hot weather this kit could cause severe pinging of the engine.
Adding the resistor makes the computer think the air coming into the engine is colder than it really is. The ECM will advance the timing to compensate for the cold, dense air since fuel does not atomize as easily in colder air. If this is done when the air is hot, it will cause a lean condition, which can lead to detonation knock (pinging). At the very least the engine will run leaner and hotter. This can cause damage to the engine. Many newer engines have anti-knock sensors, the Fiero's do not. A friend of mine in Indiana bought one before asking about it. When it arrived, it was just a resistor with instructions on a Post-It note! I thought it would be nice to inform members that these kits do not work and can damage the engine.