2000 celica gt problems please help!!!

['95hatchCivic]

gota 2000 gt 1zzfe its really hesitant when you give it gas, and wont do sshit at wide open throttle, the tranny hesitates to shift as well, i replaced the coil packs and spark plugs nothing, the obd coad reader said code
po300 random multiple misfires-thats why i changed coilpaks
p0171 system too lean- could be 1st o2 but dont want to buy it and find its not
po420-catalyst effeciency-does this mean the cat if fucked
i looked for vac leaks nothing its like the cars air fuel seems all fucked up like too much air not enough fuel also i cleaned the maf but could it need replaced. basically i cant go replacing all this stuff, to seee what works soo any ideas ask me Q's ima stay on this thread, any info on these cars helps thankss

['95hatchCivic]

any1?

[toyomoho]

P0420 is the CAT or A/F sensor. A plugged CAT could cause poor acceleration. A vacuum gauge can check for plugged exhaust.

P0171 and P0300 can be related to the same issue.

P0171 relates to the engine running too lean. If not a plugged CAT check fuel pressure, ECU coolant temp sensor.

[bpodskalny]

mass airflow sensor