1998 Lexus GS 300

1998 Lexus GS 300 Automatic 2000 miles

hello my lexus is shaking real bad when it sits for hours then I go to crank it it shakes or about ten min like a rollercoaster then when time to drive it it s=cuts o and then I i go 50to 60 miles and hour it makes a knocking ound like thump thump real loud and the speed drops and I have to put my feet all the way down to the gas pedal to pick up speed. I have been told and bought so many things and it is still doing the same thing fuel ilter was put on, sparkplugs, throttle position sensor now I was tod the cadallac converter and the timing is off. I really dont know please can u answer this question so people can stop guessing thank u
March 19, 2010.

Have the catalytic convertor checked for blockages

Dave H
Mar 21, 2010.
I had the catalytic converter check and it was block but iam still having that shaking on the car when I crank up throughout the day some people say it might be a motor mount I really dont know this time what could it be please help again. Thank u

Apr 3, 2010.
Have the motor/transmission mounts checked/replaced

Dave H
Apr 4, 2010.