wonder1and

I have had this problem for a while now and was wondering if this is common with other people... When I turn off the car and well Turbo timer is counting down... I get out of the car (idle still normal) and then shut the door... the idle will then suddenly change for some reason... either to a low idle... or a lumpy reving idle say from 500-1500 back and forth... any ideas? Thanks in advance!
Ryker