P0511

P0511 means the PCM has detected an open in the IAC valve circuit, either an open solenoid coil or a broken wire on either side of the IAC, often appearing together with stalling or refusal to maintain idle when the throttle is released. Cheapest-first diagnosis: disconnect the IAC and ohm each coil pair, a healthy 4-wire stepper reads 50 to 70 ohms per coil (Toyota), 8 to 14 ohms per coil (GM), or 6 to 13 ohms for a 2-wire solenoid (Ford); an OL (infinite) reading on any coil confirms a broken winding. With the IAC disconnected, check continuity from the harness connector back to the PCM pin (consult the wiring diagram for pin numbers), an open wire confirms harness damage rather than a sensor failure. Inspect the connector for backed-out pins, a common P0511 cause is a single pin pushed out the back of the connector by a careless prior repair, and the fix is a $2 terminal reseat. Also confirm the IAC mounting bolts are tight, a loose IAC can let unmetered air past the gasket and confuse the idle control algorithm. The expensive misdiagnosis is replacing the IAC, then the harness, then the PCM, when a backed-out pin is the actual fault.

Vehicle-specific patterns: 1998 to 2004 Toyota Tacoma 2.7L and 3.4L set P0511 from an open IAC stepper coil, the part is integrated into the throttle body on these. 1996 to 2002 GM 4.3L Vortec sets P0511 from a broken IAC pigtail at the upper intake. 1999 to 2003 Ford Ranger 4.0L OHV sets P0511 from a corroded IAC connector. 2000 to 2005 Subaru Forester EJ25 SOHC sets P0511 from a sticking IAC and broken connector locking tab. Estimated repair: $40 to $260.