i have an 88 wrangler yj with a 4.2 straight 6.  it seems to be
getting really hot under the hood.  i noticed smoke coming out of the
air filter so i took the top off.  on the side closest to the
windshield there is a hose of some sort going from the side of the air
filter (or the metal pan thing its in) to the top of the block.  on
the inside of the pan it connects to a rectangular shaped piece of
plastic with a sponge type thing in it.  im not sure what this is, but
it was smoking.  the engine coolant box and hose was also shaking, due
to the heat i assume (not really the problem but is just more info,
although is scary when there is green coolant bubbling out of the
radiator cap).
    thanks in advance to anyone who passes along useful info.