popping sounds and hesitates to accelerate ?

I have a 97 Mazda MPV, i had repairs done on the car which included replacing the muffler, Heated Oxygen Sensor (Bank 1 Sensor 1 H02S-11), the Radiator was replaced, and last Valve Cover Gasket from an oil leak which was the last thing I had done and about a week after the valve cover replaced the car was not acting normally, when i would start the car it would crank up then put off, the putting sounded like it was coming from the exhaust and under the car, this went on for about a month but the car drove fine after it started, that's not giving me so much trouble anymore, but the car is now acting like it doesn't want to accelerate when i take off, when i give it gas it putts and makes popping sounds and hesitates to accelerate and then all of a sudden it will pick up speed until i stop the car and accelerate again, and the check engine light is back on with the same code I already had fixed P1170, can you please help me decipher what my problem is?, i feel i paid way to much to get my car fixed and its worse then it was before i had it repaired. Thanks alot Tracy