Originally posted by C0NT0UR:
I just noticed that when I turn off the car, there is like a pressure release somewhere under the hood...? 
Sounds for sure like a vacuum leak of some sort. Check the IAC and the so called "Map Sensor" for leaks, as well as the EGR. Best way to tell if there is a vacuum leak is soapy water, or a cigarette. Just soak all the connections with the water, or blow some smoke around the connections. Look for bubbles, or look for the smoke to be sucked in or blown out....
