91 Civic 'Bucking'

My 91 civic hatchback sometimes shakes... Often after high RPM but not always. The engine SOUNDS like it's running great with a shot of gas....but when it idles I sometimes get this "Bucking, Shaking" in the engine


Anyone have any ideas?



Scott

Do you need to advance the timing? Just a thought..said it idled rough. Or, maybe you need to change your plugs or something. (is it missing?)

Well.. THe timing is QUITE possible... I tried to check the timing one time but I can't make out the marks on the crank pully... What about manually adjusting it... Ie... While the car's running... Is that possible?
I want to chenge it to see if that's the problem but I don't want to screw it up :)
BTW: New plugs

Does your car ever have trouble starting up? Ever any hesitation at stop lights (i.e. when the light turns green)?

Yes, Very badly when she's cold... Mostly in the winter. But when she's at normal operating tempreture, It's not bad.