Sounds like it is hitting 'rich and retard', plenty of info about this throughout this forum, but basically you probably need to start thinking about, depending on your budget and plans, a minimum AFC (apexi Air fuel controller). This is because since your pod filter was installed the ECU is detecting a larger amount of air entering the engine than normal, via the air flow meter, and is keeping things 'safe' by increasing the fuel and retarding the ignition. Not a great problem, something we all hit once the mods start.