1994 Pontiac Bonneville scan tool makes car run

I am wondering if any one has come into the problem I am having. When I plug the scan tool in the car it idles correct when I unplug scantool from the car, the car returns to the high idol condition i`m trying to diognose. The scaner give no codes. But the car returns to a high idle of 2400 rpms. Same rpm as before scanning. Could my scantools batteries be an acting ground for pcm, or what.