My 1989 ford f150.
351 windsor, seems to idle just a little ruff, then when you place in gear (auto),it's shakes slightly more.
What should I look for?

 

Do a compression test on all cylinders and closely examine all the plugs as you remove them, you're looking for color to determine if you have a single cylinder running lean(dirty injector) or all cylinders lean(sensor problem), or a mechanical problem(1 cyl with low CR).