if the idle is varying and the timing cant be set, thats classic TPS sensor. www.4crawler.com has good instructions for adjusting the TPS. Also check to make sure the throttle cable isnt too tight, that can cause it not to enter its idle mode and makes the idle vary. if it cant go into idle mode the base timing wont be able to be set. for a more "real-time" reading, i take Idl-E2 measurements at the ECU, get an ohmmeter and some piggyback test leads, connect to IDL and E2, push the gas pedal and make sure when its closed, you get the .057 reading and when you push the pedal it goes to infinite. watch what it does when you let the off the pedal.

check here to see where and how to connect the ohmmeter. this is how i figured out mine when the throttle cable was too tight, years ago. make sure you use the proper section, one is 2wd and one is 4wd. hope this helps.