The IMRC valves often fail in pairs. Despite how expensive they are, you'll be best off replacing both IMRC's if the following test FAILS:
Theory: The IMRC valves work off of engine vacuum, both being operated off the same 'trunk' vacuum tube. The vacuum line simply splits to left and right banks shortly before being attached to the actual IMRC acuators. Thus, if one of the IMRC valves has a leak, it will affect the operation of the other (even if there's nothing wrong with the other).
Try this easy test: Disconnect the vacuum tube from each of the two IMRC valves. With engine OFF (no vacuum needed for test) turn the IMRC. You will feel rotational spring tension where the IMRC wants to rebound to its original position. Place your finger over the port where the vacuum line was attached. Remove your hold on the rotating lever (IMRC) and see if it rebounds to its original position. The lever must remain in its position, proving that the internal diaphragm is intact, and IMRC is good. Do the same test on the other IMRC.
If either of the two IMRC's rotating lever rebounds while your finger is plugging the port, the IMRC is bad.
At the same time, movement of the lever should be smooth with no binding. Process of elimination diagnostics need to be performed if the levers are sticky or binding. Figure out if the binding is occurring in the actual IMRC valve or inside the intake plenum by disconnecting the rotating lever from the rod. Be careful of the little plastic clips. They break easily and you'll need to be creative with ways to substiture for them if you can't find them at your local hardware supply.
Remember that by receiving the P1518 code, the PCM is only saying that the IMRC acuator itself is stuck open; the PCM has little way of knowing whether the butterfly valves inside the intake plenum are actually moving or not.
Finally, with the engine running at idle, rev the engine smoothly from idle to a little under 4,000 rpm and down again. You should see the acuators move in relation to engine RPM. This happens regardless of engine load nor vehicle speed. Doing this test in the parking lot proves IMRC functionality. If they're not moving, then you likely have a faulty IMRC which you can test as I described above (plug the vent hole with your finger after rotating the lever).
The PCM controls the movement of the IMRC's via a vacuum solenoid. Depending on engine RPM, the PCM opens and closes the solenoid to allow vacuum reaching the IMRC's. Thus, the solenoid is an active part of the system, and the IMRC's are passive. The IMRC's simply give feedback to the butterfly valves' relative position, similar to how a throttle position sensor tells the PCM - well, throttle position.
The solenoid (in my experience) rarely fails. The IMRC's themselves are more prone to failure.
Wednesday, September 9th, 2009 AT 9:29 PM