I have a 2009 Avenger 4 cylinder i have recently have had issues with it rough idling in park if i give it gas it revs fine but then settles back down to rough idle .
When i put it in drive is shakes and runs very rough i have also noticed that the defrost heater is not blowing hot air anymore .
A friend mentioned that the engine could be blown , but i dont hear any odd noises no smoke or steam and no leaking fluid ...
Any ideas ?

 

If the engine was blown it would not run at all. Start with a general tune up. Clean the IAC and throttle body. Put some fuel injector cleaner in the tank. Any check engine light? What engine and how many miles?