2003 Hyundai Matrix fault

i have a 2003 hyundai matrix 1,8 petrol engine.the check engine warning light started to flash on and off. this only started to happen after i had service in march of this year. it started shortley after the service.but after a couple of minuets the engine started to run as it should.the check engine as done this 4 times now. but this time the engine wont pickup any more.it is very sluggish.what is causing this thanks ...ken.