Why I'm I getting a -99 ATS on the Scanmaster?

[tbirdv6]

I ran a Maft Pro on my 86 GN, when I unplug the IAT (intake air temp sensor) it then reads a 2, I've already replace w/another known good sensor, what other troubleshooting steps should I proceed with??
FRED

 

[TurboBob]

replied to your PMs at full throttle.