Typical Focus RS problem. Take the chav valve off, they don't like the twin piston dump valves. But if you insist on keeping it, disconnect the battery and leave over night. When reconnected, allow to idle with all fans and lights on to draw as much power whilst the ecu resets (sometimes helps with fast idle for a few minutes).

You can also use the Dreamscience hand unit and remove the chip and download it again.

Ensure the pipework on the intercooler isn't leaking air, because most kits on the market have too many silicon hoses and jubilees, easy enough for them to leak.

Check all vaccum hoses on the inlet manifold, these can split or pop off. Check any pipe around that area, anything seems to be a culprit.

Does it run on an aftermarket air filter? Check the pipework again to see it there's any leaks. You can also remove the MAF sensor and clean it for good measure.