90 350 TBI wont idle down.

[MotorHead Lon]

I have a junkyard fresh 350 in my 90 Silverado. When I put the "new" engine in I swapped my TBI unit the sensors, harness and everything else to the junkyard engine. When I bought the truck it wouldnt idle down when stopping and putting the truck in neutral or between gear changes. The new engine acts the same, so I'm guessing I have a bad sensor. I have had the Check Engine Light come and found a faulty temp sensor, I replaced that and a month later, while a friend was running diagnostics found the temp sensor had failed again, it was reading too hot. I have replaced the temp sensor again, and the truck still idles too high or wont idle down. Other than the temp sensor we found no other codes.

When I swapped the new engine I left the smog pump off and the truck had the catalytic converters removed. Recently sitting at a fast food drive through the truck idled down but I could smell the truck running rich.

Any help puzzling this out is greatly appreciated.