Yeo the coolant cap is a common problem Jamie.

I have seen 2 come into Triton in one day with that!

Is it local? I can come and look possibly.

I'd lose the VTA dump valve and stick the recirc back on, they sound gay, but more importantly they can screw up tha MAF sensor readings when you let the throttle off. The ECU expects some air to come past it but with the vent to atmosphere type, it doesn't go past the MAF. Hence you get pops and bangs when using them. Can also give idle probs.