When diagnosing a problem your car is having, it can be easy to lead yourself down the wrong path. There's often some element of guessing, even to good diagnosis, but if you find yourself playing a game of paper/scissors/rock to decide which part to replace next, it might be time to consult a higher power. Do you have a proper repair manual for your car? If not, you should get one right away. And don't get so stubborn that you refuse to take your car to a trained mechanic. I'm a strong supporter of doing it yourself, but if you're in the dark you can waste a lot of time and money replacing parts that aren't bad. Sometimes a trained ear is all it takes to set things straight in no time at all.