2000 Toyota MR2 2 misfires, poor idling and poor throttle r

Cel codes came up on comp indicated 2 misfires. Had so much problems with this car, new twin exit exhaust had been fitted before I bought car which was not fitted properly. Had it taken in and bloke fixed manifold that was taking in air ect and o2 sensor was replaced. He did everything he could to fix this problem ive having with throttle and idling. 2 mechanics have now been thoroughly confused by this blumin car. Im still having massive issues with idling, (only when it gets hot) the car starts shaking, and then I try the throttle pulling out of junctions and nothing happends for a while, having to keep blipping the throttle bringing up the revs then the fuel will kick in. The ecu light is on too. I put some injector cleaner in, that helped but now that seems to have cleared there's a lil power loss :-(. Im just fed up of paying ppl to sit at garages scratching their head sayin "i dont know" lol. Please help :-(