Hello mate

Firstly your plugs, the light brown is the yellow, they discolour and get covered in oil etc.

The yellow one is the collant temperature, brown is the thermo time switch. The coolant sensor is in the sandwich plate on the inlet manifold (the hardest to reach of them all).

The cold start valve is wank to be blunt. Most RS's start better without them, they tend to flood the engine, they only work while cranking from cold in any case, as soon as u let go of the key its stops. I'll put money on it not being that.

Check the basics, everything is plugged in and on the right things, theres also an earth wire for the ECU's which is very easy to miss off when connecting the battery and causes all sorts of problems!

Anything else that u can think of. If it started with your old metering head id get that back on so u can at least run it and find the fault!
If wont run your just guessing