In the process of moving to a new house our Neon SE (2.0L, SOHC) sat for about a week without being driven. When my wife goes to start it (5am Monday morning: FUN), it turns but won’t actually start. I throw on the code reader and get a P0508, Idle Air Control valve sense circuit Low. At this point, I’ve put on a new IAC valve, note: the throttle body looked good and in working order, and spliced on a new OEM wiring harness, but the pos still won’t fire up. When tracing the wires, there was no indication of them being frayed or short-circuiting. The next step, following this code P0508, would be to change out the PCM. From my research, if the PCM is truly bad, there’s usually one or several codes indicating as much; i.e. I’d be getting a lot more than just a P0508.
Could the P0508 been a red herring? I generally associated a bad starter or starter solenoid with a clicking noise, but would this still be worth checking out? On that same note, could the culprit be a bad ignition coil even without any codes showing for IC-related problems?