I had my PCM changed out (covered under federal emissions warranty!) two days ago, and I noticed since then that it has been idling VERY smoothly, whereas before, it would jitter a bit between 550 and 800. Also, when I would be going fast enough for the automatic to shift into the overdrive gear around 45 MPH and drop the RPMs down to about 1500, you would get that beautiful, low "rum-rum" sound. Since the PCM change-out, that rum-rum is gone, and you get a smooth, stable low ruuuuuuum sound that gradually goes away as it gets up in speed. What kind of problem did this indicate? I didn't get all the codes that the PCM was registering, but the ones I could see from the odometer was P0031, 37, 51, and 57, which point specifically to the oxy sensors. I immediately noticed the sound changes, before the tires got changed out today for BFG All-Terrain T/A KO tires.
Edit: black-side out.