2000 Ford Taurus rough idling problem

2000 Ford Taurus mileage: 90,000. I have a rough idling problem. Checking things over I have discovered that there is a vacuum being supplied to the EGR at an idle. Knowing that there should not be. The EGR Valve Sensor and the vacuum valve that it controls have been replaced. With no improvement, I bought an Actron 3 code scanner. The first part of the KOEO test showed 111, that it passed. The second part showed 326 (continuous memory), saying the EGR sensor has a low voltage signal. There is no "check engine" warning light. All of the vacuum lines have been checked to the best of my ability. There also seems to be a slight overheating problem that seems to get warmer after idling for a while, but it does not overheat. The engine temperature. Sensor has also been replaced. I did not continue on with the code scanner test. I did not know how to check the timing? I could not see the stationary pointer on the engine. This all started a month after the head gaskets were replaced. If you have any questions or need further in formation let me know. Thank you for your time in my problem. Any help would be greatly appreciated.