Hi and welcome to Just Answer!.
That describes a problem with your intake short runner valve (SRV) performance. The SRV is one of two tuning valves used in the upper intake plenum, the portion of the assembly that has the long runner tubes that are most easily visible from the top. Its job is to change intake runner length by redirecting air flow at the proper times, which can add considerably to engine performance.
While there is likely a software update for your engine controller (PCM) to correct the erroneous coding of P1004, chances are better that you actually have problems with the little guy. I've installed this update on numerous occasions and have had no success until replacing the hard part.
Your SRV is the one closer to the center of the engine, with the other one being the manifold tuning valve, or MTV. It's confusing and even the parts book gets this wrong, so it would pay to electrically disconnect the one I described and then check the code it sets to make sure
it affects the SRV and not the MTV.
Your PCM's complaint with the SRV is that it's not seeing proper movement when commanded to do so. This could be a problem with the actual SRV servo (motor) or with the internal tracking device, effectively a potentiometer that outputs a varying voltage signal depending upon position of the unit.Replacement is pretty quick and painless, requiring only the removal of four 10mm hex screws at the front of the unit and the electrical connector. The connector uses a red slide-lock that must be clicked to its opposite position before the thumb release is enabled. For this connector, the slide-lock is pulled outward (toward the wire end of the connector). Expect this bad boy to cost close to $350 by the way....
No appreciable effect will be seen in normal driving with the SRV disabled by the way. This unit is used above 4000 rpm and at close to wide-open throttle only, which is one of the chief reasons why we can now extract 250 horsepower from only 3.5 liters... intake tuning.
If you have any questions (like why am I typing in italics?), feel free to write back. I'll be glad to help.
Edited by Dodgerench on 7/4/2010 at 3:12 PM EST