Did you do an ecu code check? What was the result?
If no codes come back.........
It might be worth having your ignition timing checked
Make sure your temp gauge is working (so the ecu doesn't think it's cold and over fuel you)
Also check all the hoses under the bonnet to make sure they are tight and there's no signs of any holes to allow leaks.
If you can't be certain when it was last serviced, it might be worth changing a few bits, leads, rotor arm, dizzy cap, fuel filter,oil, filter air filter, (the iridium plugs if you don't know thier milage)