P1518 Code (Intake Manifold Runner Control)

I just bought a 2002 Ford F-150 with the 4.2 V6 engine and it has about 58K miles.

The Service Engine Soon light was on and the code was read as P1518 which indicated a problem with the Intake Manifold Runner Control being stuck open. The AutoZone readout says "Either a damaged IMRC actuator or an open / shorted electrical circuit".

It does idle a bit rough and pings under load.... Thoughts on what option to take? It looks like the intake manifold has to be removed to get to the IMRC. The dealer said $500+ without any diagnosis (over the phone)

Thanks