erratic running

i have a 93 saab 9000cse 2.0 16v the check engine light comes on it loses power wont idle properly and has to be driven hard to make go.It has had a new cat, lambda sensor been to the main dealer and still i have no joy ,the car is normally lovely to drive could anybody give some advice,i dont want to get rid but i am at the end of my tether please help