Truck Repair: Cummins ISB problem, cummins isb, teflon tape

Question
I had a head gasket replaced by a Cummins certified repair facility.  When they started it up immediately after the repair the check engine light went on.  Checking the engine fault code it turned out to be an intake manifold temperature problem.  They cannot solve the problem.  Here is what they have done to no avail: replaced the temp sensor (3 times); checked actual temperature of manifold (went from 257 F to -213 F); checked the conductivity of the wires (no problem found); replaced the ECM with a new calibrated one (no help); replaced the wiring harness from the sensor to the ECM (no help).  Any ideas?  I am sure the garage did something to the engine, because there was no check engine light on when I drove it in.  Thank you for any suggestions.  The garage is talking about tearing down the head.

Answer
Hello Eric,
I would make sure the ground wires are all correctly connected on the head. Possibly even run an additional ground to make sure the head, block, and firewall are all well grounded to the battery.
And a bare minimum, if any, teflon tape or thread sealer on the sensor threads.

Van