1998 Escort throttle sticking

When I push in the clutch, or have the car in neutral, it is as if you are pushing the gas pedal to the floor. It only does this once in a while and is not the actual idle sticking. I've tried adding fuel injector cleaner, but this didn't seem to help. I also noticed it gets worse if the heater fan is on. If anyone has any ideas please let me know. I am a single mom, know a little about cars and if this is something I can fix myself then I'd much rather do that.