1999 Vauxhall Astra put me out of my misery

PLEASE HELP.......where do i start..ok i bought this car 3/4 weeks ago it drove ok apart from an intimitant light that came on now and again when the light came on it would restrict its self,untill i went above 3k(rpm)then the light would go off and the car would drive fine,for a while then the light would come back on and vice vercer.plus when in 5th gear going 60/70 it would give the odd splutter as if it was the fuel filter or something i spoke to a friend who thought it was a air lock so he undone the screw under the fuel filter thinking it would relese the air(bigmistake)from then the car would take ages to start once started after puting jump leads on and towing it about a mile it wouldnt rev above 1k..so we undone the injecters once it was started to get the air out as it dosent have a primer fitted.nothing seemed to work it always led back to taking ages to start and once started wouldnt go above 1k.so i had another freind (qualified mechanic)come out after half an hour or so of messing with it he came up with it didnt have a air lock in which we thought it had he said it was either geting to much fuel or not enough fuel.(weird)so i had to get someone else out two day to do a dionostic check and wipe all the codes which were...CRITICAL FUEL INJECTION.(X 4 THAT WAS SHOWING)...HEAT PLUGS....and R.P.M...could anyone now put me out of my misery and explain what these faults are and how theyre fixed PLEASE as the man who did check/deleted, was in a rush to get home.you,d be saving me a fortune as im about 60 quid out of pocket so far.