Your problem could have started at the last cam belt change. If the chap or garage that did it got the position wrong on the intermediate pulley, this can be rectified, although the lazy way, by just adjusting the distributor to achieve the correct ignition timing. Then when the next time the cam belt is changed, all the marks are put how they should be, then the ignition timing is thrown out again. Although this should have been picked up on the subsequent road test, the garage could argue that it is not their fault and therefore charge you extra to put right a fault that was already there.
Check the marks on your crankshaft pulley and the intermediete pulley. If they are as per the book, then remove the distributor cap and see which way the rotor arm is pointed. It should be pointed to an indented line on the dizzy body, (if memory serves me well). If it doesn't, then theres your problem.
Next check the cam pully position to see if it is out by more then a tooth, although it would have to be out considerably to make the engine mis-fire.
Hope this helps when you talk to the garage.
