The first thing I would suspect is an 'open' throttle position sensor.
If there are rodents in any place you/she tend to park the truck, the fix may be VERY simple.
The symptoms almost exactly match the problem my dad's 89 supra had after a rat chewed the TPS cable- a quick rat-tail splice (heh) and some tape cured the problem and got us home, where a bit of new wire and a rat trap made a permanent fix.
I also had a FZ-6 that did a similar thing; that was a dealer recall job. the age of the truck makes me think that you're not going to be THAT lucky.
Otherwise, a trip to the local library or 10 minutes with your favorite online search tool to look up the pin-out and nominal readings for the sensor plug should enable you to check the sensor at home if you have (or can borrow) a digital volt-ohm meter.