rough idle mazda 626 1994 Es v6 egr valve replaced,problem comes and goes on 1994 Mazda 626

My Mechnic has replaced egr valve problem still there,he is still testing cleaned thottle body ,checked for vacuum leaks and distributor,and wires,he still can not find problem.The problem comes and goes,anything else to look for thank you

Asked by for the 1994 Mazda 626