Bonneville shutters in overdrive

[Green Cruiser]

My Bonneville shutters(rumbles) after it shifts into overdrive and seems to have less power(poor acceleration) It almost seems cyclic and occurs about every 4 seconds. Up a hill it really gets bad and downshifts into drive. Also, it will not shift out of drive unless I stop the car and turn the ignition off. I have changed the plugs and wires with no help. It still gets good milage. Any suggestions?

[supercharged gt]

what do you have for milage that happened to my 95 lost a coil was running on 4 cyl. pull your plugs and check them my 97 they found bad wires

[phileepo]

Originally Posted by Green Cruiser

My Bonneville shutters(rumbles) after it shifts into overdrive and seems to have less power(poor acceleration) It almost seems cyclic and occurs about every 4 seconds. Up a hill it really gets bad and downshifts into drive. Also, it will not shift out of drive unless I stop the car and turn the ignition off. I have changed the plugs and wires with no help. It still gets good milage. Any suggestions?

I had the same exact problem with my 94 bonneville ssei. The problem turns out to be a combination of bad spark plugs and using less than premium grade gas. Our bonneville will absolutely chug and gasp and clatter until we put premium gas in. Its expensive but the bonny runs a hundred percent better, and with a lot more power.