What would you expect if your manifold gasket was bad?

[gtown]

I have a 93 1.9, at highway speed 55 to 65 the engine will shake and spotter violently, I can feel it coming on and if I floor it I avoid the problem, I have replaced the O2 and cleaned the MAF, The ces light that was on and off is now off for 2 days but the problem continues. Somebody suggested the manifold gasket??