Engine stalls

Sometimes at idle, the engine with shut down but will start right back up. The check engine light will come on momentarily. No codes show up. Other times, the engine will stall at highway speeds momentarily but then will get back to normal. Again, the check engine light will illuminate momentarily but no codes. So far, I have had the IAC, camshaft position sensor, crankshaft position sensor and two spark coils replaced. Still doing the same thing. The dealership says the engine wiring harness needs to be replaced but they cannot find one. Any suggestions?