This may sound strange, but this is a legitimate question: does your Monte get picky when it comes to ignition keys? For some reason whenever I try to use my rubber head key the ignition won't budge, but when I use my regular metal key it works perfectly. Both keys are cut exactly the same but for some reason my car won't accept the rubber head key. More amusing (personality quirk of the car) than anything, but has anyone else had this happen?

 

I have had these issues before. My metal key has a small head and the rubber one is large. I know that my dash was sticking out a tiny bit further then it was supposed to so when I would put the rubber one in, it would have trouble going in all the way so technically it wasnt in the hole the whole way. So it would not turn and work. My metal one is thin so that one goes right in and works fine. I did realize the rubber key was much shorter as well but this rubber one was aftermarket so maybe that is why it was so much shorter compared to the metal aftermarket one.

 

The key that doesn't work has worn down so it doesn't set all the tumblers in the switch.