90 legend runs rufffff!
 

I have a 90 legend ls and it has been sitting for 8 months. My father did a tune up and changed all fluids, various cables and the battery. it drove fine for five miles and BAM! Rough idle and accelleration. the whole car shakes but when you do reach the speed you want it rides ok. Thought it was the cat converter because of acceleration loss and rufness but it still runs bad. When in park runs smooth, as soon as you put in d or r it put put put's. please help I spent $700.00 so far and i just want to fix it and sell it. I also put fuel injector cleaner in and nothing.