we reciently replace the bearing housing for the idler pulley and the 3 serpentine belts. after doing so, now the check engine light is on and has no power, and is sputtering and missing. we also had to replace the radiator because of a busted connector. we got the vehicle to a parts store to have it coded and it came back as 2 upstream o2 sensors and a misfire on number 5. we took the it to the local chevy dealer because there isnt a kia dealer anywhere close. the service dept said that whatever was causing the misfire was what was causing the o2 sensor code. they checked spark plugs, wires, coil packs and fuel injectors. finally came up with it being an injector on #5. that was changed and they say that didnt fix the miss. they have not changed o2 sensors for some reason and say that it couldnt be the timing belt. also they say that it has an exhaust leak (runs really quiet). never had a problem with exhaust before. any thought please??