BMW of Shrewsbury

I got a check engine light as I came off the highway, it rode a little rough to a gas station. I filled up and started the engine. It rode smoothly home, no check engine light. Out of an abundance of caution I called my BMW service center for an appointment to check it out. It drove smoothly to the dealership, getting it up to 80 mph on the highway. No check engine light. Eventually I was told it was the Vanos unit, it has 2, so I agreed to change both. One of the 2 new units was “faulty “ so they needed to order a new one. On the following Monday I was told it looks good, just need to road test it. Afterwards, I was told it now has a faulty fuel injector and maybe replace all the plugs and coils. It sounded crazy that BMW’s diagnostic test didn’t pick up a faulty fuel injector or coils or plugs. Eventually I was told it needed to be walnut shell blasted ($10,000) or a new engine $27,000. But they would buy the car from me for $4000. When I picked up my car I was told it ran fine unless I “punched it”. It’s a 445 hp, twin turbo V-8. As I drove it off the lot I got it to 25mph and it shook violently. I couldn’t get it past 25 mph all the way home. I called the dealership and explained what was happening as I drove it. Much worse now after $4000 in repairs than before I bought it in.