How do I trouble shoot the Idle Stabilizer System?

The Idle Stabilizer System on my 88 GL causes the engine to run in a
jerking fashion. When I disconncted the ISV (idle stabilizer valve) the
jerking stops. Re-seating the ISC (idle stabilizer control) - behind the
right rear tail-light did nothing, nor did cleaning the ISV thoroughly.
Consequently I have been running with the ISV disconnected, but I really
want to connect it back up since 1) it stabilizes the engine on cold
starts, 2) boosts the rpm when the power steering limit switch kicks in
and prevents the engine from stalling when I turn a corner, 3)  boosts
the rpm to prevent the engine from stalling when the A/C kicks in.

All input on this will be much appreciated.

Thanks,

John Rodgers
88 GL Driver