Hesitation and ISV

[ozitzmann@atmi.com]

My '90 200Q has a hesitation at part throttle (less than .7 Bar) when the engine
is at operating temperature.  If I am driving at constant speed, the car feels
like a bucking horse.  The hesitation is in a very rhythmic manner (about 1
every second) and feels like the engine has shut down.  If I let off the gas or
give it more, the hesitation goes away.  I have disconnected the ISV and the
problem is gone.  The car idles very well with the ISV connected and not well
with it disconnected, so I don't think the ISV is the problem.   I have cleaned
it, but that made no difference.

Does anyone know what might cause the ISV the apparently cycle at part throttle?

oz
'90 200Q Avant