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What is the year make and model of the vehicle?
2002 dodge ram 3500 van 5.9L.
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Remove the 4-wire connector for the Idle Air Control (IAC). Attach a test light to battery ground. Start the engine, probe the four circuits while revving the engine up and down. The test light should blink on all four circuits. If it does, attach the test light to battery positive and re-check each circuit again. Once again the test light should blink on and off on all four circuits. If one or more circuits are not blinking, the wiring or the Powertrain Control Module (PCM) is at fault. If they are blinking the IAC is bad. Test the wiring between the PCM and the IAC for open circuits or for short circuits. Repair as needed.. If the wiring is OK, replace the PCM.