1997 Skoda Felicia

hi, i am pretty mechanically minded but i am well stuck!, engine pausing/hunting quite bad on acceleration and runs generally poor, although very occasionally it will run great for a day or so! ive changed the fuel filter, air cleaner element, plugs, new inlet manifold gasket, timing chain is a bit rattly but havent done that yet, cleaned injectors, checked throttle body for signs of an air leak, checked wiring connectors, it seems like its something really simple but i cant pin point it !! please could you give me an idea? thankyou....steve shaw