Cadillac Repair: 1988 ElDorado loss of engine power after.., catalytic converter, throttle body

Question
My mechanic just flushed the cooling system, installed an idle modulator, and put in a new gasket under the throttle body.  Now the car has NO power.  It starts and stuff, but is just dead.  HELP, it's been 3 weeks.  What could he have done?  Is there a way to resent the computer?  Any help, hints would be appreciated.  We are pulling our hair out and don't have a lot left.

Answer
Did you check to see if the exhaust has a restriction such as a plugged up catalytic converter ?.

IS or HAS the CHECK ENGINE light ever illuminated while driving the vehicle and or has any other lights illuminated or any messages from the message display center ?.

What work or diagnostics of ANYKIND WHAT-SO-EVER have been performed on the vehicle trying to fix this problem ?.