Hi Andy
I have exactly the same problem although my ex-partners KA misfires really badly at all speeds. Feels like it is firing on just 3 cyls. I originally thought it might be fuel. I pulled off the hoses leading to and from the fuel filter located just in front of the fuel tank on the near side. Then un-hooked the fuel lines to the fuel injectors to see if fuel was being pumped through - it was.
Then erplaced the plugs (watch it the KA is prone to plugs siezing). I have bought some leads to replace the existing ones. What I'll do is take a lead off at a time to see which cylinder is misfiring. The leads are ciold sprung by the way so should just pull off. They are a sod to get your hands on though being located right underneath the engine.
If all this fails I am told to get a replacement coil pack - but now we are talking money and after all she is only my ex-partner!!!
Paul Tilzey
July 2008