Depollution light?

Hi everyone peugeot depollution system faulty driving me mad.
Took it to dealer said it was either petrol pump, chain, all cost arm and leg . So took it local garage change chain and check pump all fine light still on don't know what to do..... Put data clean still same. Looses power so I just turn off ignition turn on rev for a few sec and drives a treat this has been going on for months car drives lovely once warm. Please help.