Thanks everyone for the replies and feedback. Finally got a chance to look into this over the weekend. Sure enough found that rodents had chewed on the wires in at least two places between the connection to the differential and where they disappear into the body, right through the grey sheath and the insulation for both wires. Wrapped the bare wires with electrical tape (separately) and then tucked them into some split plastic conduit and cleared the code. Problem solved? Nope; Started right up and ran like a champ until I got about half way to work, felt a few hesitations, but made it to work ok (18 miles, 1/2 highway). After work started up fine, maybe a few skips on the highway, then about 5 miles from home it died on me as I let up on the gas for a red light. Coasted into a driveway. Cranked fine but no start. Waited about 3-5 minutes and then it restarted fine. Made it the rest of the way home with occasional skips and stutters. Code 3-1-1 is back.
Speedo/odo/ABS appear to be working ok. CPS was replaced (bougicord) at the 250k timing belt change 10k ago, so doubt that's a problem but will put a spare in just to rule that out. Looks like I'm going to need to check that wire farther up to see if there are more shorts. The Mrs is very consolate but somewhat indulgent.