IAT 2 Step Not Working- Minimum Spark Advance

I am trying to get my 1990 Mercedes 190E that has an L67 with 66mm turbo to leave better off the line. I am attempting to set up the IAT 2step mod that i have seen some of the v8 truck guys use. The ecm is a p04 out of an early 2000s Regal/Grand Prix. I set up the IAT base correction to pull 30 degrees of timing when the IAT is reading open -38 degrees and hooked the IAT sensor return to a momentary switch. When I am logging, I can confirm the IAT is reading -38F when switch is activated but my timing wont go negative past 0*. Is there a minimum timing advance table I am missing or is the ecm maxed out at 0*.