Tony.b

My 96 Sti type RA was running fine until I took it for a routine service at 47k miles. Car is all standard with no mods. Air and fuel filters were replaced along with spark plugs, but it was returned with a misfire when accelerating above 5,500RPM. They had put in BOSCH FR5DP1X plugs, where it previously ran BOSCH FR6DP1. They then tried a further set of the same plugs which were no better, and said the front plug on the left hand bank was fouling up. Compressions tested and fine. An attempt to replace ignition leads made it worse. He then put in NGK plugs and it is running smoothly again. The mechanic suggested I replace the ignition leads to the left hand cylinders, suggesting that this may still be an underlying problem, but I don't want to spend on a good set if this is not required. Anyone know the difference between the BOSCH plugs, and were they suitable? Should I replace the ignition leads or is there something else I should check? Finally, can anyone recommend someone in the Harrogate area to service my car?