94 LS 400...High idle after major tune up

[yardbuzzard]

I performed a major tune up (cap, rotor button, plugs, and wires, throotle body cleaned). Now the idle spead is about 1200rpm. I can tap with something hard like a screwdriver on the idle air control valve body and it will fall to about 650rpm's and run perfectly until the car is turned off...then back up to 1200rpm's. . Tech said the gunk on the plunger of the IAC is coated with carbon and can not retract. He insists it is internal and can not be cleaned. Over 600 bucks for the part!!!
Question: Can it be cleaned?
Will something like Seafoam or other fuel injector cleaners eventually clean the plunger?
Any suggestions would be appreciated.
thanks in advance.
Bill from North Carolina

 

[Lextreme II]

You can test the ISC using a meter here ISC and clean it with carb. cleaner.

 

[yardbuzzard]

Great info...any other schematics of associated efi parts?
thanks