Hi Scatz - yeh I hate to throw money at a problem just to find out its something entirely different.
Maybe we can work together and figure something out - let's review the situation.
1. Does the engine misfire all the time or only at idle
2. Is it worse when cold or warm
3. Does the engine start easily
4. Any signs of backfire via the inlet manifold or exhaust.
5. Any warning lights on the dash
6. Have you checked all the plugs to see if they are all the same colour
7. Any hissing sounds when ticking over
8. Does the engine sound like it misfiring when idling or haunting
9. Is the engine using any water
Yeh a load of questions but it may help us rdeuce the possibilities
Ok...here goes....to the best of my ability;
1. Assuming that a misfire would create a sudden rise/fall in revs then it misfires mostly when at idle although there are occassions when the car jerks whilst travelling, mostly at a constant speed.
2. Doesn't seem to matter be it cold or warm.
3. Engine starts in the morning perfectly, however, if the car has had a sudden case of the erractic revs and subsequently stalled, then I have to keep the key turned and my foot on the gas, taking a while sometimes (5, 10, 15 seconds maybe). Leave the car for a couple of minutes and come back and she starts first time again.
4. Very slight backfire through the exhaust although I would say more of a 'pop'.
5. No warning lights, apart from the obvious STOP light when it stalls.
6. All the spark plugs are brand new (one of the things I paid out for to rectify this problem).
7. Cannot say I have noticed any hissing sounds.
8. You can feel the car slightly judder every now and again like it's misfiring when at idle, although not constantly (don't know what you mean by 'haunting').
9. Water is fine, no loss and no mayo in the expansion tank.