Limp mode and p2100 fault code AGAIN!

Hi I'm really hoping someone knows about this issue or can help... 

I've got a mk2 2005 1.6 petrol focus sport. Every few months it goes into limp mode and throws up a code P2100 - Throttle Actuator Control Motor Circuit/Open. 

Sometimes I can fix it by clearing the code or disconnecting the battery but it still comes back, as well as a full service its had new plugs, new leads, new lambda sensor. It's going back in next week for its yearly service and I'm asking for a new coil pack to be put on. I don't know what else to do, from other forums I've seen people replace the instrument clusters, throttle body, throttle position sensor, the wiring looms and still say it's not fixed, then the forums go dead. Ford just want to keep changing parts which I can't afford to do. It was fine after the plugs and leads were changed but then I hit a puddle and the same code came back, dried out after a day and again was fine, put a new better quality air filter in last week, ran fine then the next morning into limp mode, got it out, drove about 3 miles and then back into limp mode... Has anyone ever come across this? Thanks in advance - Ryan