I took advantage of a sale at AutoZone today and bought an Innova 3100RS scanner for $125, they're $200 direct from Innova. I hooked it up to my Ranger and let it idle. The long and short term fuel trims are more or less 0%, with some intermittent -2% readings. The catalytic converters were also reading 99.2% efficient, for a 22-year-old Ford with 274,000 miles, I'd say that's pretty impressive. I noticed an oddity while looking at my live data. The Timing Advance at idle fluctuates around 2-5 degrees ahead of, and behind 20 degrees. I've always noticed an intermittent touch of a roughness to the idle, but it doesn't seem to really bother anything and has never tripped a CEL.  There are no rattling sounds like a worn timing chain will make. I've heard the 3.0 has issues with its camshaft synchro on non-distributor motors, which the computer uses to set timing via the camshaft position sensor on top. Could a wearing synchro gear be causing the varying timing? Revved up and held, the timing stabilizes itself.