EGR Valve, where is it located? (Random Misfire)

I am have a Random Misfire and this is part of my troubleshooting process.
I wish to locate, inspect, & possibly replace the following:
• spark plugs, ignition wires, coil(s)
• Incorrect ignition timing
• Vacuum leak(s)
• Low or weak fuel pressure
• Improperly functioning EGR system
• Defective Mass Air Flow Sensor
• Defective Crankshaft and/or Camshaft Sensor
• Defective Throttle Position Sensor
• Mechanical engine problems (i.E.—Low compression, leaking head gasket(s), or valve problems

The odd thing is that I did not have this issue until the day after I went to DEQ and they plugged their computer into my car or the timing could be a coincidence.