My car has been "shaking" for 1 year. Various mechanics have checked, they all end up replacing the same parts thinking that is the problem. One mechanic told me it could be the manifold (excuse me if i'm not spelling correctly). Which I bought from a junk yard, but haven't had anyone inexpensive to replace it for me. Any suggestions as to what may be the problem. There are days it shakes more than others, and is more like a slight shake, especially when it i idle. HELP PLEASE