If doing trackdays please carry a spare set of plugs, as I have lost hundreds of pounds and lost track time by not having them, please learn by my mistake.
The reason I say this is below (a few posts I pulled from .org, which can tell the history)
I have a track focused 2.4 with Harrop SC
26/10/21 In 2021 I had a misfire for a while and it was a dodgy plug (from poor fueling), even though they where changed gaped and checked to be working out of the car. Also I suspect the metal heat sink pack that's ontop of the coil pack (sorry can't remember it's proper name), as I think this had a dodgy connection as it connects to the coil pack.
I did have a spare coil pack but it did the same, I tried disconecting that separate pack ( with the heat shield on) ontop also and clean connections.
I also removed the plug caps from the coil pack (the cows udders), these pull off and there is a small metal rod about 12mm long that a spring makes contact with, this inturn contacts the plug. One of mine was pretty rusty, it might not of been the problem but worth cleaning up.
Also my TMAP sensor was also reading 60 degrees too high, so changed this also. I had a few issues at once unfortunately.
You can see this on the Dutch software. Try running a log when car is stone cold and see what temp it is reading, if the car is cold and not been run, it should read ambient temperature. This TMAP sensors are in the SC cars.
Good luck, it drove me crazy.
28/10/21 I replaced the TMAP, changed and checked all the plugs, changed the coil pack with a spare. Started it and it ran great, thought it was fixed, took it to the rolling road guy as it was already booked in for diagnostics. Then when I joined the motorway, at 3k the misfire started again and by the time I got there (30 min journey) it was so bad it ran on 3 cylinders.
1/4/22 I just wanted to follow up on this thread to stop anyone else wasting there time and money like I have. I have just gone to do my first track day this year and it was ruined again as I had a misfire. I did the usual and changed the coil pack and cleaned the connectors but it still misfired. I was meant to get a set of spare plugs after the last incident but never got round to it. On the day I couldn't get any plugs locally as these are cold ones (Iridium Denso ITV27) and so I had to pack up and go home with a tear in my eye. So 200 odd pound on the track day, 70 in juice there and back, a 2 odd hour drive there and back and wasted day because I never bought spare plugs. I am kicking myself. I remember after we discovered it was dodgy plugs the tuner set the fueling up so that it was safe but required another tune as it was over fueled. I had did 2 track days and had a mechanical issue after the first (oil leak due to crank shaft pully coming loose). Then the winter came and it slipped my mind to take it back to be tuned.
So if your doing track days regularly please order and carry some spare plugs, so you can rule it out. When my plugs arrived 2 days after my trackday it ran like a dream...