See if you can pull codes from the computer system ('87 will not light a "check engine" light). Some sensors are not used until it goes into closed loop. Could be ECT, o2 sensor, failing TFI, etc. But check the computer for codes (particularly CM) first before replacing anything.
1987 Ford Ranger Short Bed 5.0L/T-5 Project
1988 Ford Ranger Long Bed Parts Truck
1993 Ford Tempo 2.3L OHV HSC Auto - D/D Stock.
1999 Honda Accord VTEC Auto
2002 Dodge Caravan - 3.3L Auto