engine management light?

i have a 51 plate peugot 206 which passed an mot in february the engine management light now beeps constantly after going to a garage i was told it was only spark plugs which they replaced drove round the corner it was chugging and revving on its own i was then told the lambar sensors needed replaced another 150 quid still no joy it shakes revs i was told to use red ex ........some1 else said injectors i really have had enough of being fobbed off any1 help!!!!!!!!!