2000 BMW 328 Engine Shakes

I have a 2000 328i and it has been giving me a lot of trouble. Sometimes when I am driving it will begin to shake terribly, when I stop it only gets worse. It also seems to have trouble accelerating, like there is no power behind it. These two problems normally occur at the same time. Adding to the list, it also smells like something is burning. While it doesn't happen all the time, the problems seem to be more frequent. I have taken it to the dealership in Fort Walton Beach, FL but they tried to say there were no major issues. They said my check engine light was on because of past misfires but everything was fine now. On the drive home, the light came back on and the problems were still there. I read a little on the internet and found that someone whose problem was almost identical to mine needed to replace the ignition coils. Also, do you think I should try to find a mechanic who works on BMW's instead of going to the dealership again? They seemed like they were too busy to deal with my problems. Any thoughts?