Q: I'm not sure what is wrong with the car and I don't want to pay a ridiculous amount for a diagnostic check.

Hello. You can try taking your car to a local auto parts store and have them plug into the scanner to see why the Check Engine Light is coming on. It may give you an idea if what is wrong, but may not give you a complete answer unless thoroughly scoped out. A fault code will give you an idea as to why the light comes on but doesn’t always give you a solid idea of the repair needed to solve your problems. Diagnosing why a vehicle is having symptoms often requires following a diagnostic tree. After getting information from the fault codes, there is a process of elimination that needs to be conducted. "Check ABC. If ABC checks ok, then check DEF. If DEF checks ok, then check GHI. If GHI does not check out ok, then replace XYZ." In your situation, since you are having multiple problems, I would insist on having an expert diagnose the vehicle, instead of blindly replacing components. This will ultimately save you time and money in the long run.