2004 focus air/fuel mixture problem!!!

I have a 2004 focus with 112 k miIes.. recently my car started to have issues.when i start the car it starts up and runs for 2 or 3 seconds and the engine dies out.it seems like the car doesnt isn't getting gas. im not sure but my check engine light is on now!.

my friend pluged his computer into the cars computer and it said (error- air/fuel mixture metering) pIease i am wondering what could be wrong with it.! can it be a fuel pump or what? and how much will it cost me?

Clean the MAFS mass flow air sensor. Get MAFS cleaner spray can from Advance Auto and spray it on, let it sit 15 minutes then spray it again. DO NOT touch the tiny wire with ANYTHING! I think it takes a 20 secure lock driver to get it out. Advance should rent them.