engine problem

well, put water in my cracked radiator and started the 240, to see how it would run. at idle, the engine rocks side to side, real hard. rev it up, and it settles down. let it go back to idle, and it starts rocking again. my first guess is a rod knocking, but there is no knocking sound. was also told motor mounts. anyone have any ideas?

start the engine w/ the hood open while it is idleing unplug one plug wire at a time (at the valve cover) and see if the engine stumbles if so then that one is fireing move on to the next. If you find one that when pulled nothing changes then you either have no fuel or no spark or bad compression (compression is not likely unless it's a bent valve also not likely) pull the plug and look and see if it is fauled and if it is wet, if it is wet go ahead and check for spark if it sparks (plug it in with it out and hold the bolt part of the plug to the valve cover or a ground) if it sparks it's fuel also if it's wet it is most likely fuel. Pull the injector and swap with one of the others if the problem follows the injector then the injector is bad if the problem doesn't then you have something fuck up somewhere else but it is MOST likely fuel or fire on 1 or more cylinders.