99 Silhouette shuts off if gas pedal is not depressed

[4stevis]

My 99 Silhouette 3.4l just developed a new problem. In order to start the vehicle you have to press down on the gas pedal and keep your foot down or else it cuts off. A little history....I've been having an intermittent idle issue. Sometimes after the engine is at operating temp on a day when the outside air temp is >70F, when you come to a stop the engine rpm would ramp down as with a normal deceleration then the rpm's would spike to about 1100 rpm's then back down to idle rpm's then spike again about 3 or 4 times until the engine cuts off. Once the engine is restarted you would have to press the gas pedal to get between 12-1500 rpm's or else the oscillations would re-occur and the engine would quit again. I've replaced the Idle Air Control Motor, and thoroughly cleaned the intake air horn and flapper, I've replaced the PCV valve and ran the codes in the computer: The codes were a possible purge valve, or a possible vacuum leak. Im leaning toward believing a worsening vacuum leak is the problem. Anyone have any ideas???

[Tech II]

Leaning towards a vac leak....