Hello, new here but i have a 2008 xc70 and i have been having issues that i can't seem to get resolved.

had my car do something weird when i pushed her pretty hard to get into traffic. A weird WHOOSH sound and it ran until i got off the highway and pulled into a parking lot where it shut down. After trying for several minuets to get it running i got it to run enough to get to a parking spot. I removed the battery cable and gave it a couple of minuets, reconnected it and it started right up and got me home.

I next rented a code reader and it had a fuel rail pressure sensor fault. I replaced that and it kept throwing the 2 lean bank codes. I took it to a mechanic and he replaced the PCV box (oil separator) that had a torn diaphragm. I thought i was good to go but......................70 miles and a potty break later check engine light is back on. Same lean bank codes (Po171 P0174) Took it back to the mechanic and he changed the battery, and did a smoke test and found a couple small air leaks replaced a couple of o rings to fix the air leaks, and same thing. The care drives fine runs good but when i start it every day or 2 or 3 it will not want to start and idle and will die several times until i can get the rpm's up to 3000 or so then it will start to run and i can drive it and it will clear up and run good. one other thing my gas gauge is now acting up. I "broke down" and my fuel gauge showed over 1/4 of a tank. i put gas in it and it started right up.

I have done some research and am leaning towards the fuel control unit. Thoughts???? how is this confirmed/diagnosed Do i get to it from the bottom or from the top? they are $300 What are the thoughts of getting a used one from ebay or such?? Thanks for any help.