2 things. I don't know how, but our local Precision Lube put in 30 oz. too much when we recently got a tranny fluid change. Take out extra fluid that could damage the tranny and cause vibration.
Second, since the idle screw is glued in position, I got some lead (that's right, Pb) tape from the golf shop cut some small strips to built up the choke plate arm (about six strips thick) where it meets the idle screw to increase the idle. Getting it up to about 1400 rpm in Park will give you 1000 rpm in gear when at a stop. The engine stays smooth. | 
