[ChevyTech]

Repair any wiring issue at the front of the intake.

The ECM and engine sensors ground at the front of the intake manifold under the front intake bolts/studs or by the thermostat.

The computer uses the coolant temp to determine how much fuel to inject and how fast the idle speed should be.
The coolant sensor the computer uses is by the thermostat.

Make sure all those connections including the coolant sensor connector are in good condition and tight.

There is also a ground wire between the back of the passenger side cylinder head and the fire wall. It would be a good idea to make sure it is in place.