My MFI RS Turbo has been sat a while and while it started straight away after standing it had a bad miss and was overfuelling very heavily.

Nothing has been messed with since it was running fine.

I have put new plugs and leads and what not on it and it made no difference.

The car will idle perfectly with the fuel pressure actuator plug off off, but then of course you can't rev it as the metering unit is returned to limp mode I think.

Also noticed that the car will now run with the oil cap off, which it definitely did not do before...

Would you suspect the metering unit itself given that it runs fine with the plug off or the fuel ECU or something else?

I'm clueless to be honest so if anyone can help please break it down for me as far as possible lol