If your Fiero has had a strange problem, and you have found the solution, post it here.
Here are two related problems I had. These could occur on 87 or 88 dukes (maybe earlier ones also).
Problem 1: The temp gauge goes up and down a few times until the car is warm. It looks like it may overheat, and then drops down.
Cause: One of the heater lines is connected to the underside of the intake manifold, and water flows through the manifold to get to it. It is connected by a quick-disconnect fitting that has a build-in restriction in it. If the water flow is too restricted, you get the gauge bounce.
Problem 2: Your car is fully warmed up on a hot day, and you stop at the store, shop for 10-15 minutes, and find that the car won't start, or runs briefly and then dies.
Cause: The water flow described above is not restricted enough, and the throttle body has over-heated. This can occur if you remove the quick disconnect (which often leaks) and put in a standard fitting with a hose clamp. Temporary fix: Spray starting fluid on the injector. This will cool it down, and the car will now start.
Solution for both problems: Replace the quick disconnect with a standard fitting, and install a "heater control valve" in the line, as shown in the picture below. Adjust the valve until neither problem occurs.
