Okay so the first time it started to misfire and throw the error code 21 I swapped the OEM coils out with brand new yellow jackets coil packs and replaced the spark plugs with brand new NGK iridiums at approximately 80,000ks. The yellow jackets stayed in the car for around 10,000ks until the car started acting up again. I contacted the supplier and they had informed me that they must have had some kind of malfunction, I sent them back and had another brand new set sent out to me under warranty. Had the new set installed and the issue was fixed again.. until now... I have now done approximately another 10,000ks and the problem has arisen again. The car is a 1999 r34 25gt-v (rb25de neo). I bought the car with 77,000ks on the clock and since then I've only driven around 30,000ks. It now sits on 113,000ks. Is there anything that would be contributing to the coil packs failing? An underlying problem perhaps? Anyone with similar issues?