It says code 11 is for alternator. However I dont see how that would cause your car to shake but rather not start or stay running, unless it is just on the edge. I have a 95 and the dealer can read my codes without a problem, You need a new dealer if they told you they cant.
I would suggest you check your vac hoses for leaks and clean out the carbon build-up in your engine. These could easily cause a rough idle or a loopy idle.
