Ford Repair: crown victoria (police car), coolant temp, coolant system

Question
1999 crown vi that idle surges when stopping. and at idle. also scan shows coolant temp at -40. has been to couple dealers and now i have it. have checked iac, egr, has steady 21lbs. vacume.  

Answer
Hello and thanks for the question...I'll try to help.
 Since your ECT (Engine Coolant Temp) sensor is reading
-40, that would be a problem right off the bat. This is causing the engine to run rich. I would replace the sensor and then clear the codes with a scan tool (if any are present). I would also suggest that you replace the thermostat.....it is just a good practice when opening the coolant system.
Hope this helps,
Erik