Z71 350 5.7 Engine Flooding

I need help please. I recently had the Intake Manifold Gaskets replaced on my Z71. Now every time the mechanic tries to start my truck it floods and dies. My mechanic went through reconnecting the distributor and found two wires crossed. Moved them back to the proper place and retimed. Still would not run. The computer would not set a code for a few days then finally set an ECM code. We replaced the Spark (Knock Sensor) but this has not fixed the problem. Now the computer is setting a code 42. I don't know which sensor needs to be replaced and would appreciate any information as to which way to go from here.

Thank you. DJ

What year is the truck? The control and injection systems are a bit different depending upon the year.