I had a problem appear late last year with my car (was fine for about 5 months), as it started to misfire at high boost - circa 27psi+. I fixed it by buying a new set of NGK 9's. The car has been standing for several months and when I took it out a couple of months back for a quick blast it started doing it again very slightly, but occasionaly harder when hitting that kind of boost.

Now the plugs have only done about 300miles so I can't see it being the plugs, but I did take the later set of NGK 9's out and used an older set for getting the car in and out of the garage, until the better whether came for proper driving. I now have the newer plugs back in, but I never cleaned them when storing or when I put them back in the car.

I was told some time ago that these types of power conversions can suffer from misfires at high boost and such things like Jacob's Ignition systems can help.

NGK 9 Plugs are at standard gap
I have motorsport leads on the car (new last year)
The dizzy cap and rotor arm was replaced last year
Coil is the original one
If I turn the boost down to around 26psi it is fine - but who wants to run at 26psi when I have a spanking new T4 to trash the nads off!!!!

Should I have cleaned the plugs up after storing them? If so what should I use to clean up NGK 9's cause the tips are delicate.

Any advice?