What is wrong with my Peugeot 307 1.6 petrol?

I bought a peugeot 307 1.6 petrol 2003. It has been running fine until a few weeks ago. It wouldn't start up so had to push/jump start it. Then last week, I went to go for a drive but it wouldn't rev up past 1.5k. The engine warning light came on and anti-pollution fault sign came up. I've done the test that comes up with codes. 1st code was P0123 (bought a new rev pedal, it worked fine. Drove about 5 miles, turned engine off then it happened again) Did another code read and it came up with code P0121 ( bought throttle body, fitted it but it didn't make a difference) Done another code test and it came up with P0123 again but that can't be the problem as we already tried that. What else can it be?