Some further information in regards to testing the solenoids that control the intake manifold swirl plates / intake manifold runner control:
The solenoids look like this, and are located next to the cylinder head, on the passenger side:
One solenoid actives the IMRC and the other one activates the IMT / Swirl Plates.
Each solenoid is supplied by vacuum from the intake manifold. When commanded 'on' by the
PCM, the solenoid will then send this vacuum to the IMRC / IMT actuators.
The most common problem we see on these solenoids is a P2008 code, Intake Manifold Runner Control Circuit Open Bank 1. The problem often starts of as an intermittent fault and is well documented here on the forums.
According to the workshop manual, "the solenoid for the intake manifold switching system is supplied with either the maximum voltage or zero voltage, i.e. the valves are either fully open or fully closed. Actuation depends on the engine speed and the engine load." A definitive test for the solenoid would be to manually supply vacuum to the solenoid (eg a hand-held vacuum pump with a gauge), and then supply voltage the solenoid (ie. command it 'on') using a PowerProbe or similar, then watch the vacuum suddenly drop / bleed off. An alternative, quick and easy test would be to actually switch the solenoids over and see if the problem rectifies itself.