I have an occasional misfire usually at low revs when under power. Its never cut out or failed to start. Sometimes it goes months and then reappears. Changed plugs and it seemed to disappear for ages.Checked codes (with a simple tool) last week and there was nothing stored. However, yesterday it was bad for about a mile with no acceleration and the engine management light came on. Then it recovered and is running fine now but the light is still on. Removed the plugs and I'm pretty sure no1 was not as hot as the others and it looked different. I have been suspecting the coil rail (but its hard to diagnose without individual coil packs) Been quoted £70 for replacement. Should I risk it ? but as its running fine again I may not see any improvement. If thats the problem would the light go off or need re-setting ?

(Also read about wrong grade oil causing valve lifters to stay open etc?)

many thanks, Mike