Check engine

Check engine light came on at 120km and fix it.light back on took to shop to check my 09 e350 sedan.mechanic said manifold has to be taken out and some plastics break due to heat. Cost me $550.00 light back and car misfires at some points and check engine light flashed or stays on.I brought it back to shop they said a coil failed and they replaced it. Just picked car back today and light is back on after a few hours.