The air induction system improves engine performance by using the intake manifold runner control (IMRC) assemblies as follows:
The intake manifold has two runners per cylinder, feeding each of the
intake parts in the cylinder heads. The IMRC assemblies are located
between the intake manifold and cylinder heads, providing two air passages
for each cylinder.
One air passage is always open and the other passage switches from
closed to open by means of a valve plate. Below 3000 rpm, this valve
plate is closed to improve low-speed and cold engine performance.
Above 3000 rpm, this valve plate opens to improve high-speed engine performance.
This is what you hear as your car hits 3400 rpm's; the "secondaries" open
up. If you can't hear this on your car, and your SHO seems a bit
slower or sluggish, your IMRC deactivation motor may be damaged.
It will need to be replaced to bring the SHO back up to speed again.
The valve plates are opened and closed by the IMRC deactivation motor, which is controlled by the powertrain control module (PCM).
The IMRC deactivation motor has been known to fail, causing poor performance at wide open throttle. Some tell tale signs are 16 second 1/4 mile times or the absence of hearing the secondaries open at part throttle at 3,400 rpm's. In some cases, the cable that controls the IMRC deactivation motor breaks or the wheel inside the IMRC deactivation motor housing has broken. In either case, verifying if this is the problem is a simple task. However, it requires replacement of the IMRC deactivation motor. That procedure will follow.
Procedure for replacement of IMRC Deactivation Motor is forthcoming.