Random limp mode

i put all of my savings into buying a newish car around 8 weeks ago. I had a timing belt fitted and a service done. I knew there were a coiuple of faults on it by the codes. These were 0500 vehicle speed sensor and 0380 glow plugs. Then about 3 weeks ago i was doing around 30mph when the car just slowed right down and it didnt matter how much i pressed the accelerator pedal it wouldnt go above 1000 revs. I turned it off and turned it back on and it was fine.Read the codes 1122 and 1120 then at random it happened again a few days later. Took it to a mechanic who said couldnt find a fault and wiped the codes so he could see what came back up when it went into linp mode which it did. 1120 and1122 came back again and another code for the immobiliser 1614 ( i think). so he said to replace the pedal. I wasnt sure it was so took it to an auto electrician who read the codes again and rang me and said he thinks its the edu or ecu but couldnt be sure without stripping it doen. I really really need help with this. Its far too close to xmas and i have emptied my bank account on this car now. I cannot afford to throw money away on fixing things that arent broken. I would appreciate any help . Sorry about the long post