Toyota Repair: 2000 celica gts misfires and is sluggish, 2000 celica gts, air intake hose

Question
Ted i'm writing to see if you have a solution to this problem: In the mornings when my car is cold it barely shifts with out almost dying and even when at tempature it miss fires and once up to about 3000 rpms just boggs down and is sluggish. i will be going 70 mph on the highway and when i hit a hill it drops to 40 mph. I just changed my serpentine belt and spark plugs and even the spark plugs didnt help even a tiny bit. i also checked in the dark to start my car a see if i could see any sparks from the plug wires from hair line breaks, but they looked fine. my car has 125000 miles and am thinking it could be fuel injectors. when i read my code readings it ran PO171(system too lean) and PO505 random or multiple cylinder misfire) its a 2000 celica gts six speed. thank you in advance.

Answer
The PO171 code is caused by the mass air flow sensor, it's located in the air intake tube just after the air filter, replace it to fix the 171 code, the 505 is an idle speed malfunction not a misfire code, replacing the maf sensor may take care of both problems but I would recommend removing the air intake hose from the throttle body and thoroughly cleaning the inside of the throttle body with a stiff brush and some spray throttle body cleaner, once all the gunk in the throttle body has been cleaned and the MAF sensor replaced it should take care of the problem.