i felt like each mechanic was ripping me off, so i kept going to different ones.
You have no idea about what IS wrong with this or how the system even works, but automatically assume because the car isn't perfect that you were ripped off. You initially bought the car at an auction, which I need not even go into as the others have taken the words out of my mouth. It died out and did not have the battery power to restart so you had it towed. Your first mechanic diagnosed a bad alternator and made the repair needed to make it run.
The amount of money i have spent on it, i want to get it fixed and drive it for at least another year.
A perfectly understandable thing to say. We all want that from our vehicles. Jumping from one shop to another isn't making a lot of sense if you are trying to do it.
volvo dealer- said wrong alternator was put in, and said it will cost 4k dollars to 100% fix it.
I would wonder why you didn't bring it back to the original mechanic who already has your money from the first job and get this remedied. Also, ask Volvo why the alternator is wrong. Are they saying it because it is from a parts store instead of directly from Volvo with a Volvo part number? Why is this a $4000 job for an alternator only? I've never seen one that expensive even with labor in my life. An estimate like that deserves and in fact requires clarification.
3rd time- took the car to a mechanic because it was shaking in idle, taking longer to start, having a longer turnover. This is what i got from the mechanic,
Ignition coil (AA) E371 ------------$45
Spark Plugs (AA) APP3923 --------------$24 for six of them.
So he found weak spark because you needed a tune-up and had a weak coil. While that alone was not all you needed to make this perfect, it was what he was able to find wrong and remedy for you.
The mechanic also wanted me to get "right side half-shaft, tires, control arm bushing (both) and rear pads and rotors. But i didn't.
Ok, this was a very bad move. If that halfshaft breaks you will be stranded with a car that won't move. Inconvenient but not dangerous. The control arm bushings are getting play in them, and if they get any worse are going to make this car handle dangerously and be difficult to control. Last but not least, you are willing to spend $4000 on an alternator to make it run but refuse to do a BRAKE JOB!! That is like walking up to every single person on the same road as you, giving them the finger and saying "I don't feel like keeping my car safe and don't give a damn if your friends and family have to die because of it." You have no right driving something with marginal brakes on a public road. I don't care one bit if it runs like crap until that is fixed. Going is optional, stopping is not.
One thing to bear in mind is that auction cars sit for quite a while not being driven. No telling how long this one sat around. With the ethanol in gas today. it has a third of the storage life of gasoline without the ethanol. You haven't really gotten to drive this very much since you got it, and you might just have some bad gas to work out. Get a bottle of Chevron Techtron additive and a full tank of fresh gas, then run it around a good bit (after you get those brakes put on) and see if it helps. Its not a magic cure, but may give some benefit.
Volvo vehicles are in with the other Euro cars in the way the are built. They use different tools and are designed differently than american and asian cars. As such, you need to be going to a mechanic that specializes in european cars. He is going to have the specialty tools and scanning software along with a familiarity with the particular problems these are known for. Think of us like doctors, some are general practice (basic maintenance, exhausts, brake and suspension), some specialize (driveability techs, transmission techs). So when you have an issue you need the right guy. You wouldn't go to a proctologist to find out why you keep getting headaches right? Even though he went to medical school, the way he is used to diagnosing something would be to say the least unpleasant for you and you may not get the results you want.
You don't have to go to a dealership only. You need to find a shop that specializes in euro cars. The ones that do usually only work on them and nothing else. They make sure their advertising lets you know that this is all they do. There are far too many things that could be causing your problem. None of us are going to be able to tell you with any certainty what is wrong, but we all know you need someone who knows this car line well.