More Idle Issues

[Kracka]

From everyone's good friend, Rick Shindley:

I worked on a '91 today that had bad idle surge. I checked the ISC
motor and cleaned the throttle body for starter. No affect.

I cleaned the BISS and checked its o-ring. No affect.

I removed the ISC motor and disassembled it. No problems found.

I reset the idle switch (throttle plate stop). No affect.

Finally, I removed the throttle body (again) and disassembled the
fast idle air valve. It was black with carbon. Rather than risk it
not working, I replaced the lower throttle body assy with one from
an old '95 throttle body (I didn't have a 1G TB lying around). It
worked!!! The FIAV was stuck open (apparently) and wouldn't close
when the coolant to the TB got hot.



Rick