1996 Nissan Maxima Engine turns off

I recently started experiencing a fnny situation with my 96 nissan maxima where the engine just shuts off if i'm in stop and go traffic or sometime when I am slowing down for a stop light. The car also shakes at about 65mph but I am not sure if they are related since I do also have some ball joint issues. Anyways I took it to the mechanic who did a diagnostics and said the only code that came up was for the knock sensor but he couldn't guarantee that that is the source of the problem. I am not sure if to go for the almost $600 repair cost which might not correct the problem or to get a second opinion. Please help