Having serious problems

Well for starters my engine light came on before I had baught my car... One of the deals where when I purchased it was what ever was causing the light to come on must be fixed. First they fixed it and it came back on I took it back they sais it was the battery connection they fixed it light came on again shortly after. So I took it back once more and they said it was now an 02 sensor. After that never came on again, however it had been acting shady and recently stoped Idoling so I took it to someone else they said it's a tps switch... So i was wondering any one know what might go next or if they may have cut the engine light switch off cause even after my car stopped idoling the engine light never came on!