I would suspect an induction boot leak. Very common on BMWs. Get a spray bottle full of water and spray from the manifold out to the air fliter while revving the engine at 2000 rpm or so. It should stumble if you are near the leak.
Frequently happens when someone doesn't properly tighten the clamp to the manifold or the one to the airbox, and sometimes the rubber just cracks and it is hard to see.
It's worth at least ruling out.
__________________
'99 4Runner SR5 5spd 3.4L V6 4WD(U.S), original '99 Talls in front, OME 906s in back, Hella fogs, Trekmaster shocks in front, Billy in back, no running boards, FIAMM horns, Alpine sound, Michelin LTX M/S2's, owned since new.
'97 HiLux SW4 5spd 4WD(Japan model bought in Brazil assembled in Argentina, very close to a 3.0 4Runner/Surf)
'71 FordWillys Jeep CJ5 (with straight six Ford Maverick 3.0 liter engine--lives in the mountains north of Sao Paulo Brazil)
My Backyard Frame Swap
