P1518 means the IRMC micro switch inside the IRCM module is not being made as the runners close. This is because the runners are carboned up as already said.
Best thing to do is to wire them open and forget about having secondaries. Or clean them and make it a 30k normal maintenance job.
DTCs P1518, P1537 and P1538 indicate IMRC is stuck open. DTCs P1512, P1513 and P1519 can indicate IMRC may be stuck closed. DTCs P1516 and P1517 indicate IMRC input error. DTC P1520 indicates IMRC control circuit malfunction.
Possible causes:
Cables improperly routed (binding) or seized.
Damaged/disconnected IMRC housing return springs.
Lever/shaft return stop obstructed/bent.
Lever/shaft wide open stop obstructed/bent.
IMRC lever/shaft stick/bind or disconnected.
IMRC actuator cable/gears seized.
For electric IMRC, view cable routing. Make sure cables are not binding or improperly routed. With key off, cable core wire at IMRC housing attachment must have slack and lever must contact Closed Plate Stop Screw. For ******/Tracer, view IMRC actuator lever. Make sure lever is visible. For vacuum operated IMRC systems, make sure sensor linkage is attached and secure. Lever must contact closed plate stop screw with key off. Also, make sure IMRC sensor harness connectors are attached to the proper bank. They are interchangeable. If necessary, use a breakout box to pin out the harness connectors to the corresponding electronic EC pin. Refer to the IMRC System Description in Section 1A , Intake Air and Throttle Body, for illustrations.
Note: IMRC return spring is strong. Make sure return springs operate properly and plates open and close fully.
Manually open and close IMRC plates at intake manifold (press IMRC lever down for ******/Tracer) and feel for sticking/binding.
