I would replace the ECT(engine coolant temp) sensor just on speculation
Its a cheap sensor, which you can test but.........just easier to replace
It will have 5 volts on 1 wire
3 volts on the other wire when cold
1 volt on this wire when fully warmed up
Computer uses/needs ECT sensor to set the CHOKE on a cold engine so it can start and idle until it warms up enough to not need to be choked, about 5 minutes
In the old days a carburetor used a metal "choke plate" on cold starts, fuel injection can't use that setup so the computer must set "choke mode", rich fuel mix, high idle, advance spark timing, which it would only do if ECT sensor showed cold engine temp
Dash board temp gauge uses an ECT SENDER, 12volt unit, no connection to ECT sensor(5 volt) or computer