Horrible missfire

My car has developed a horrible misfire only on very tiny throttle opening, holding a certain amount of rev’s, if i can describe it that way. Put in new plugs, any other thoughts

A Backfire is usually the combustion of unburnt fuel/air mixture exploding in the exhaust or exhaust manifold.Reasons are possibly sticking exhaust valve (compression stroke is forcing unburnt mixture out of cylinder) or maybe a duff sparkplug or sparkplug connection causing the unsparked mixture to be expelled.

Another thought would be to check the ‘usual’ stuff for misfiring - ignition leads/coil may be iffy [although this would affect it all round the rev range] or it may be the ECU putting the wrong fuel mixture at certian points.Take it to your local dealer/specialist and get the fuelling checked, perhaps on a rolling road or summat, and see if that throws anything up.I dont know much about Exiges, or a lot about the K-series block, but general info like the above applies to all cars anyway, so its worth a shot.