Toyota Repair: Tercel wont turn off, fuel air mixture, combustion chamber

Question
88 Tercel. When you turn off the ignition, it continues to run.  

Answer
This is known as dieseling, the fuel air mixture ignites by compression alone without spark, it is primarely caused by a carburetor malfunction, it has an anti-dieseling solenoid that is supposed stop air/fuel from going into the carburetor, it may be malfunctioning, it can also be caused by an idle speed that is too high, another cause may be that there is a lot of carbon built up on the pistons and the combustion chamber, this raises the compression.
Try using the highest octane gas you can get, if that helps the problem there is too much carbon in the combustion chamber, if there is no improvement the problem is with the carburetor.