chamber system pressures

[CTDiesel at aol.com]

Does anyone have ideas on the following diagnosis?

First let me say there are no vacuum leaks!
My 4kq does not like differential pressure between chambers.  When there is
any mA current at the DPR the car doesnt cold accel without stumbling and
irregular idle, until the 02 sensor kicks in.  When in closed-loop all is well.
HOWEVER, I have the DPR set at less than 0mA  it cold accels very well and
smooth at idle and seems perfect.  BUT when the 02 sensor kicks in, the car
stumbles up to 2000 rpm then takes off like a dragster. Idle is smooth though.
I saw in the archieves that ~10mA at DPR is ideal.  What though determines
the current at the DPR, Altitude sensor? O2 sensor?
Anyone with ideas and thoughts would be appreciated.
In many talks with folks nobody seems to know what causes this problem.

TIA
DJ