Innova 5135 code reader will not read codes?

I bought an Innova code reader to help diagnose my problem on my truck. It won't read any codes. I get it plugged in as the book says, but it won't read any codes? I can hear a couple of relays clicking, yet on the reader itself I don't see the "down triangle" showing it is communicating with the EEC-IV? Nor do I get the square before it gives a code? It will then (the code reader) shut itself off? Should I get a test light and try the method you have at the top of your article? I replaced the MAP Sensor, the pressure fuel regulator, the idle bypass valve, and the check engine light still comes on and it is hard to start and idles rough.