You may need to run some quality fuel system cleaner through the car. Two cans of BG44K can make a world of difference. You have to go to a car dealership parts department to get it though. It costs around $20 a can. It is well worth it as it removes so much sludge that it will make the car run funny during the two tank fulls of gas that you use when you put in each can into each tank of gas. Then after a third tank of gas you will notice a differrence. It takes some time for the computer to re-adjust too.