Hey everyone, I'm new to this site so please forgive me for not knowing how this really works yet. Several months ago I bought a 2000 Volvo S40 and it ran great up until this point. In the past couple weeks it has started to vibrate a lot during acceleration and even just idling. It also has less power and the engine is very loud and at the max I'm getting 11mpg. I am a pretty aggressive driver however I think that the mpg should still be better than that. Also the car will not stay running after sitting or when its cold. At first I just had to give it gas while turning the engine over and it would start, now I need to hold the gas down to about 2000 rpms and take it for a drive or else it will just die. I have ran some dry gas through it and it didn't help. I'm not a car expert but I do have some ideas about what it could be, however, I would like to hear your opinions on parts I could change that would fix the problem and increase performance? Also, if I take it to a mechanic and they run diagnostics, what would that tell me?

Thanks!
Adrian

 

Difficult without basic diagnostics!
Airflow sensor faulty would be on top, but let someone check the basics.

 

Check for fault codes first.
That narrows down the list of possibilities consideably.