It doesn't matter Korean or us ECU. There are things that must be programmed to work correctly. A competent mechanic knows to pull the programming off the old ECU and install it on the new one. How will the new one know the codes for your immobilizer for instance. You are blaming your car for what sounds like a bad mechanic that has no idea what he is doing or is purposely breaking something when fixing another. It's pretty simple when you go through your system. Your need fuel, air, and electricity. I diagnose my car by smelling the tail pipe and listening/feeling the vibration from the engine. If you smell gas but no vibration it's running rich check air issues. Get vibrations then it's either electric or fuel. I can go I to more details of how to figure it out old school or talk to a old mechanic and he or she will go on and on. You really need to take your car to someone that knows new cars and even better a Suzuki or Chevrolet dealer. I know they charge way more then this guy, but do you really think they would have started replacing part after part after part. It is possible that you never fixed anything in your car for way too long and they are all going all at once but you didn't need a mechanic to diagnose everything if you know how to do basic stuff on your car. Paying for all the parts and doing it yourself in a few hours would be way cheaper then paying someone to try one thing at a time charging you again and again for diagnostic. When I didn't know anything about cars I was told this. If replacing injectors, coils, spark plugs, wires, fuel filter and air filter yourself could save you the diagnostic and you are basically doing a tune-up so why do you need to take it in when it will cost less in the long run?

Parts are very cheap. One thing I didn't deal with is ECU. Now that I have an expensive diagnosis tool and I've learned a few things I'm able to, but if they slapped the new ECU in without plugging it into their computer then you need to bite the bullet and take your car to a dealer. Get all the parts they removed from the car to take their and they can fix what was actually wrong then you can go to court to get your money back from this other mechanic if he doesn't refund you right away.