whats wrong with this thing?
 

The car is a stock 87 gxl
I was driving home this afternoon doing about 60mph, when I attempted to go a little faster I felt somewhat of a hesitation, the car started running like it was missing, (if it was a cylinder engine). When I got off the highway at stop lights it wanted to cut off, so I had to stay on the gas. It kind of smoothed out the higher the rpms. Taking off from a stop is horrible, it shakes and slowly gets up to speed. When I got home it would idle at like 500 rpm and shake violently. I changed the plugs and now it wont start, any help would be appreciated because Im new to the rotary. Thanx

check the compression, first ...

I got the car running now, but it still shakes. Engine runs and revs smooth but shakes. Could broken motor mount be the cause? I kind of hear a clank noise and see the mount vibrating, is this it?

Swap your primary and secondary injectors you may have an injector going bad, had similar prob. with a customers car, (Dirty injectors).

glad you got it running now ...

well 2 things ... (1) when was your last full tune-up? (2) check for vacuum leaks ...