[Tom Goldman]

The problem you have with a large bore single blade is closing it far enough to get it to actually slow down the air flow enough .
I have closed the throttle of some EFI Stock Elim .cars to where the TPS is at 55 -60% and all that happens is we loose a little 60' but the car actually makes it back up between the 330 and 660 clocks.
Like Lenny said you need to go closed farther , maybe not to idle but I would say at least down to 25-35% open . ... .when you try to slow a small amount of E.T. ,It becomes more difficult to maintain control of the RPM .
I would try going out farther on the first number in the timer , maybe at least past the 60' before going on the stop. that will allow you to run the second timer a little longer.
Also you should be running an open loop , Closed loop will just play hell with the car at part throttle.