truck wont idle all of a sudden

[beamn7]

Check the vacuum line to the map (baro) sensor. They used to use a black plastic line that was prone to cracking and leaking. It connects to the passenger side rear manifold vacuum source on the carb. Seen the line to the sensor full of fuel before which would sometimes happen during a full throttle application. Usually only on ones that the line came out and dropped down low before heading up to the sensor on the firewall. Easy fix is to "T" the sensor into the manifold vacuum source port on the manifold behind the carb and plug the port on the carb. For a quick check, unplug the vacuum line to the MAP (baro) and the carb, and then blow through it to make sure you don't have any fuel in there. Then plug one end and blow to see if you have a leak in the hose.

Could be a failed MAP (baro) sensor also. If the ecm looses the MAP (baro) signal the mixture control solenoid pulls the metering rods down causing a lean condition via the idle air bleed valve and the vehicle stalls at idle. Unplugging it like you did causes the mixture control solenoid to stay in the "rich" position which will allow it to run / idle. The 85-86 CA emission trucks with E4ME carbs use what looks like a MAP but is actually a baro sensor and works opposite of a MAP. If you plug a standard MAP in (plug is the same) the truck will not run properly either...

Hope this helps.