2003 Dodge Ram Van 5.2L P0505: IAC Valve Causes Engine Stalling and Idle Choking
My 2003 Dodge Ram Van 5.2L is experiencing severe idle issues with a persistent P0505 fault code. When I temporarily disconnect the Idle Air Control (IAC) valve, the engine stalls immediately — it chokes and shuts off completely. This behavior occurs even after replacing the oxygen sensor (O2), removing the catalytic converter due to ceramic debris damage, and performing full exhaust cleaning. I've replaced the IAC valve, rotor, distributor, spark plugs, and the last O2 sensor. The engine previously ran smoothly but suddenly began stalling under idle conditions. I've also tested with two different ECU units — both exhibit identical behavior, ruling out a faulty ECU as the root cause. The P0505 code is triggered when the IAC valve is unplugged, which suggests a malfunction in the IAC system or its control circuitry. However, this issue appeared suddenly and without prior warning, making it difficult to diagnose. I'm seeking advice on how to properly troubleshoot this problem — especially whether there are other related fault codes present (such as P0999+), if live data from the engine is available via my OBD2 scanner, and what diagnostic steps should be taken next. Any guidance on fuel pressure testing, vacuum readings at 150 or steady RPMs, or IAC wiring continuity using a digital multimeter would be greatly appreciated. Thanks for your time — this has been a frustrating issue to resolve. Art
Make sure your OBD2 scanner can detect all fault codes, especially those above P0999, and that it provides live data such as engine RPM, intake manifold pressure, and fuel trim values. The symptoms you're describing — stalling when the IAC is unplugged — suggest a possible IAC valve or wiring issue. Recommended diagnostic steps: - Perform a fuel pressure test under normal conditions, then check for pressure drop during a KOEO (Key Off Engine On) cycle. - Conduct a vacuum test at 1500 RPM with the engine running steadily; if intake manifold vacuum drops significantly, it may indicate a leak or faulty IAC operation. - If you're comfortable, use a digital multimeter to check for continuity and voltage in the IAC valve wiring harness — ensure there are no open circuits or intermittent connections. These steps can help isolate whether the issue lies with the IAC itself, its electrical connection, or another underlying system failure.