My Daughters 91 300ce Did Same Thing. Took It To Several Dealers. Finally I Fixed It. New Motor Mounts, Oxygen Sensor, Ovp, And Look For Bad Vacuum Hoses.

She Cannot Believe It Is Same Car When She Drove It. It Took Us A Year Of Fooling Around To Finally Have It Smooth Out. I Think Motor Mts And Oxygen Sensor Helped The Most.