My question is this :
Did you tell the mechanic to change those parts,,,,or did the mechanic tell you he was going to change those parts ?
After he changed the first part,,,what ever that was,,,did the car run correctly,,if yes,,then this could mean that your car needs a whole lot of work and money because it has had its life and now its time to start replacing parts.
Now if the car did not run correctly after the first part was replaced,,,then who ever is working on the car is guessing at what the problem is and as long as your willing to keep paying the bill then they are fat and happy like a christmas goose.
Its time you ran that car over to the dealer and had them look at it rather than the fly by night mechanics you have been using so far.