[ChevyTech]

The old gas could be a big part of the problem.

If the coolant senor ground is poor it will cause a cold temp reading which will cause the system to be to rich. The ground is to the front of the intake manifold. The ECM also grounds at the front of the intake.

If the MAP sensor ground is poor it will cause it to go rich. You said it made no difference when you unplugged the Map sensor. You should test it.



MAP sensor testing TBI

Manifold absolute pressure sensor

Do you have a hand vacuum pump for testing the MAP sensor?

A normal Map sensor reading on the wire that connects to terminal “B” (possibly Lt green) would be 1 to 2 volts at idle. With no vacuum to the MAP sensor the voltage should go to at least 4 volts.

NOTE: if it runs poorly it could have much lower vacuum at idle which would cause a higher voltage reading.

Terminal “A” (possibly Gray) is voltage supply to the Map sensor. (Should be close to 5 volts)

Terminal “C” (possibly purple) is the ground for the Map sensor. (Should have no voltage)