That's the idle air control valve opening up for some reason, probably a code is being thrown. Don't force that valve open or closed as they are easy to break. Does he have a check engine light on? I had the same symptom when my TPS was wired backwards and I had no ground to my O2 sensor.
The plate on the bottom of the intake is bolted on, and is infamous for leaking. It sucks oil into the intake and will cause increased oil consumption that increases over time. With a flashlight, you might be able to see oil streaks on it by looking down a wide open throttle body. Engine off of course... Hughes and several others make a complete kit to upgrade the seal. Be careful over-torqueing the intake bolts!
There are some knowledgeable trouble shooters on this board that may chime in.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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