My father's 92 5.7 (pickup) has a horrible miss at idle. When you start the truck cold, the idle will surge up and down for quite a while. If you put it in gear and try to drive it will stall. The problem has been traced down to the map sensor. If we unplug the electrical connector from it, the truck idles fine. As soon as the connector is plugged in it chugs and hesitates and the idle goes crazy. We bought a new sensor today and it still does the same thing. Any ideas? This truck has had the 305 replaced with a 350 and all the wiring, TBI unit, sensors, and computer as well.

 

Anyone help?

 

sounds like a egr problem, stuck open. or possibly the throttle position sensor.try taking off the egr and seeing if there is carbon stuck in the port, or check to see that there is resistance at the tps.

 

unplugging the map sensor should force the ECM to go full rich, so that might point to a fueling issue. How does the spray pattern look at the injectors? Have you checked your fuel pressure? Also a lot of ignition problems will rear their ugly head at idle. Everything in good shape?

Are you getting any codes that are not related to you unplugging a sensor?