Re: 1989 stalling/guages not working
Start checking electrical connections. Engine grounds, batt terminals, reseat as many harness connectors as you can get at (including the ECM).
I had a similar problem with my '90, identical to your symptoms (particularly the strange gauge readings, like the speedometer and temp needles jumping around when the car was sitting still.). In my case, it turned out to be the ECM, which I replaced with a junkyard ECM. 45k miles later and the problem has never come back. Never threw a SES lamp or stored a code..car just did bizzare stuff, quit, and restarted like nothing happened. But with all things electrical and bizzare, start with trying to get a trouble code out of the ECM and re-seating connectors.
As our cars get old, it'* handy to cruise the junkyards for a spare ECM to have on hand. They are cheap and easy to come by..and it'* handy to have an ace to play when strange stuff starts happening.