MX5Ireland

My car has a slight misfire in it, replaced the spark plugs yesterday and it slighty improved but when sitting idle the revs are constantly dropping, is this a common problem? The spark leads in the car aren't that old and they are aftermarket red NGK as far as I can remember.

I know all cars revs slightly drop below 1000 when on idle rev but it is very noticeable on the car.

Any advice would be great

im in the same boat myself i repaved the leads after giving the plugs clean and still no joy which is leading me to believe a coil or distributor problem

Most lightly to be the coil !! We have several types are there are different amounts of pins on the actual coils themselves depending on year ,size etc

just fixed this problem in my own car.
recently i changed the leads and plugs and it went away, but not completely.
it started to get worse so i changed one of the coils, the one that controls cylinders 1 &4, at the same time i pulled all the plugs to check them and found a cracked insulator on one of them.
i replaced them all and its back to normal at last.

If the leads have been replaced anytime recently it nearly always the coil/coils as the tend to overheat a bit where they are positioned on the engine.New they are a fortune but we have good used ones for sale. In saying that I have a few lads in the UK that actually keep a spare coil or two in the boor just In case ......so it speaks for itself really....minor issue really and easy to fix at low cost.........so not bad for oldish car........