My 2007, 70K mileage, Saab 9-3 throws a P0300 code. The engine runs very rough at idle time. If I press the gas pad little bit, then the engine runs much smoother. The engine runs fine if car is running until it stops. So far, I have done following things, changed all 4 coils, cleaned/changed MAS sensor, cleaned throttle body, swapped throttle body with a used one I got from eBay, none of them made any different. All original parts are looking clean and in good shape to me , so I put all original parts back. Now I am thinking to look into vacuum leaks. The first thing I found is there is a hose seems goes nowhere and one end of it doesn't connect to any part. I have taken some pictures. See below. The hose is colored in red. Can anyone tell me where this hose should be connected to. The picture hose3.jpg was taken while I pulled the hose up so you can see it isn't connected to anywhere.