I sort of had the same problem with my parent's car. I was told that for some reason LS motors tend to "jump timing". Not to sure if that's true but here's the deal. My cousin and I popped off the valve cover and for some strange reason, the markers on the cam gears were off and the belt seemed a little loose. Well, my cousin put the car back together and it still didn't run right. The car kept on bogging. So I got fed up with it and checked the timing again.. And it was still off since he didn't check the marks on the cam gears. So after I set the cam gears right, the car started up and was fine. But here's food for thought. My uncles '88 Honda Prelude doesn't start. I checked his timing for hours and it still kept on slipping. I've heard of Ludes having bad tensioner bolts. So I concluded that was the problem. But instead, some people are saying it's the fact that the Lude has a bad water pump which is causing the tensioner bolt not to work right. There's food for thought..