check engine light

hey..my check engine light comes on everytime the truck is stopped at idle in park, but when u put it into drive and drive away within 5 seconds the check engine light goes off. I come to realize that i have a huge hole in my exhaust pipe and a hole in my muffler on my 94 jimmy. Could that be the reason why my check engine light comes on?

I am no engine expert, but it could be the exhaust is getting back into the intake and making the mixture jacked up.