87 caravan, strange sound when cold

87 caravan, 3l V6 engine
When starting from cold, it has a very lumpy, and uneven idle. generally, if you shift it to drive, it'll stall, even with your foot
down. when i was doing some work on my headlights, adjusting aim, i was cranking up the engine, to refresh the battery, and noticed a sort of heavy 'roar' coming from the right of the battery, where a previous owner has put a fan on the air intake. It does however look like the intake goes down a lot more (some sort of stock CAI maybe?).
a quick blip on the throttle, from the outside, and it kept the revs up for a few moments, the roar increased, and then, after about 10-15 secs, went back to its lumpy tickover. blipped it again, and it revved up, roared up, and then when it dropped, it dropped to normal idle, the roar was gone, and the vehicle was driable.
anyone know whats going on?
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