I had the same problem on the KA24E, but i was silly and took off the whole thing without buying a gasket to replace it LOL. I found out however, this method would work and wished I did it.
On the SOHC-
Locate the idle adjust screw
Unscrew completely, be sure to apply some pressure on the screw while unscrewing, there's a spring, dont lose it.
Spray your favorite cleaner in there
Replace screw and adjust your idle back to normal
WOOT
^_^
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