My car is as old as I am. It used to belong to my grandpa, and it just recently fell into my hands as a Christmas present. The heater is busted, but I think thats out of my skill and financial level right now. The engine has trouble starting up every now and then, I think thats an electrical problem because when it happens I just throw it in neutral and it starts up right away. When I'm idling the engines RPM fluctuates, and I can see the tachometer slowly move up and down. Once when I was idling, the engine came to a stop. Also when I'm idling in Drive, the car shakes pretty violently. The first time I filled up the tank at the pump, I noticed some sort of grimy build up inside and around the threads of the gas cap.
Is there any kind of fuel additive or solvent I can use to make it run smoother, and maybe clean out some of the internals?