The manifold pressure sensor disconnected will throw a P0400 code. Problems with the resonance flaps will throw a P0200 code.

I would first look at the EGR valve and confirm operation. It sounds to me like the intake diverter valve may be asking for exhaust gas (and possibly not getting it), and when you hit the throttle, it opens back up to the main air filter box. Just a guess though.

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Mark in MA
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