I recently redid my harness for my 5.3 swap because it wasn't clean enough for me. It started fine but it drove very odd. I did get p0102 on the obd2 and my IAT is reading at -39°. My wires are all good and I saw someone that had a similar problem so I took the ground for the IAT and soldered it in to another ground that I knew was good but still nothing. Same problem. I am getting 12v and 5v at the connector. Never have had this problem but it seems pretty common.

Any help is appreciated
-Jesse

 

Ok I figured it out.
I was using a LS3 maf sensor so I had a connector that converted the 5.3 maf to the LS3's. I turned out that the two pins were bent so I fixed them and it still wouldn't read. I used a jumper wire from the iat ground and the iat signal on the 5.3 mad and it jumped from -39c to 140c. So now that I confirmed my signal was good I jumped two wires from the 5.3 maf plug straight to the pins on the LS3 sensor and I got 33°. So something happened between the connectors, but I have no idea what because they were very high quality. Anyways I looked at an LS3 MAF pinout diagram and a 5.3 pinout MAF diagram and labeled each wire A-B on both sides. Then I cut the connectors off and soldered them to each other. And I still got that 33° reading.

Really do hope this helps!!
-Jesse