Heyo, I've got a 1988 FC vert that's got this weird problem, that kinda comes and goes away at times. It kind of idles a little rough, and when I go to add gas, it just surges, like rises and falls. It may be simply coincidental, but it started doing it again when I accidentally let the fuel drop a little too low, as in a little under a quarter tank. I think it may have something to do with either the TPS, the AFM, or just simply sediment in the gas tank that needed to be run through. I'll try and search for new things, and try to adjust the TPS, as well as examine the fuel filter that is in it. I'll keep trying to update with things I might try to troubleshoot.

 

checking the tank for rust and sediment are a good idea, also inspect/replace the fuel filter sock. A new fuel filter on the frame rail wouldn't hurt, especially if it's been on there for a while. If you notice a lot of sediment, there's a good chance that you have a dirty injector causing your idle issue. When the car does idle, where does it idle at?

 

When I get it to idle atleast decently, it's at about 900 smooth. Cold it sits at about 1500 till it's at temp. the surging happens at about 2000-2500 while applying throttle.