If you have a second key to the vehicle, see if that will start it. The system is misreading the key. If not, the system must be diagnosed. Most often is the key reader, though can be wiring and/or the BCM. Make sure it goes to someone that can tackle this system
4.3 vortec 5speed s10 98 idle rising when truck coming to stop, cyl.#1 misfire and map/barp circuit...
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4.3 vortec 5speed s10 98 idle rising when truck coming to stop, cyl.#1 misfire and map/barp circuit high input pending codes from scanner at auto zone