Blazer won't shut off

[Phydeux]

Need help! I have a 1990 full size Chevy Blazer. About two months ago the problem started where when I turn off the ignition and remove the key the engine continues to run. I replaced the ignition switch and am still having the problem. I even disconnected the ignition switch and my alarm completely and it still continues to run. The alternator is only two years old.