HOw can I fix my Opel Astra Wagon 2003 model?

How will I check if I made the right timing. I already brought the car to an authorized shop and have it scanned. but they said that there was no error. I am not not satisfied with the idle. I had my mechanic check the valves and it was okay. But when he returned all what he removed, the engine start but there is no idle and CHECK ENGINE light appears on dashboard. How can I check if camshaft and crankshaft sensor are working? The engine has been repaired. We replaced the cylinderhead assembly with good second hand and we grind the valves, replaced piston and piston rings, rebore the block to 0.50mm. Even the main and conrod bearings were replaced. so practically, I overhauled the engine.