engine managementlight?

i have a vauxhall vectra1.9cdti engine management light keeps coming on have hadit checked fault exhaust air mass sensor new sensor fitted, light comes on again air con fault although air con not in use system reset.driving again on comes e/m light goes into limp mode again system checked fault accelerator sensor new sensor fitted system reset,next day driving
e/m light comes on again car goes into limp mode turns
engine off waits 5-10 mins restarts engine drives o.k gets back home .driving me mad as to why e/m light keeps coming on after so long driving yet to go a day with out light coming on