The Intake Manifold Runner Control (also sometimes wrongly known as the swirl valve) is somehow getting stuck in the wrong position. Possibly it's become sooted up, or its vacuum bellows is faulty, or the bellows linkage is seized, or the ***ociated Frequency Solenoid Valve is leaking (or its air admittance filter is blocked). If you delete the P2017 does it come back immediately? It's no big deal, by the way, primarily an emissions control mechanism.
Using the forum search facility for 'P2017' (with the 'forums' button selected) brings up loads of results...
