I had the same problem a while back. No hot exhaust out of one pipe, rough idle, poor mileage. The cause was a intake manifold leak at the five/six runner. Suckin air instead of fuel. Engine seemed to run good at higher speeds but would not idle right. Your problem is on two cylinders that don't share a common runner. Pull spark plug wires off one at a time while the engine is running at idle. The ones that drop engine speed when pulled off are making power and the ones that idle speed doesn't change are not. This will confirm you are having problems with two and three and not one and two. Then spray a little WD40 type product (flammable type) on the intake runner where it meets the head and see if engine speed picks up.
Good luck, Gael
