Impala SS only runs right w/ scanner
 

Hey guys,
I recently purchased a 2008 Impala SS knowing it had some electrical issues. Here's the story; guy I bought it from said car worked great until he had a "mom and pop" shop replace the transmission. After that, it developed electrical issues where the car will only run correctly if it has a code reader plugged in to the obd2 port. When the scanner is plugged in the car runs normal with no codes or issues. When the scanner is unplugged, the idle starts to wonder up and down then I get a "service stabilitrak" message along with u0073 and p2544 codes. The traction control light also flickers on and off (it is not consistently blinking). From what I've looked at, it should be a ground wire that is loose or pinched some where. I've tested all the grounds I can see and they check out fine. I've also read it can be a faulty computer but the dealership service records he provided me say that tests on the ecm and tcm came out good. I'm sure there's something I'm over looking. I have very basic knowledge of electrical stuff so bare with me. Thanks!