P0125 code

[RockNBronco96]

Recently my '96 started idling fast, around 1200+ RPMs, this wasn't a slow increase it started in an eyeblink. (351 Windsor, AT, A/C) I checked for loose vacuum lines and electrical connections and found none. Finally my engine light came on and gave me a P0125 code, I've done some research but have a couple of questions before I try to tackle anything. I run a 180 or 185 degree thermostat, which this time of year takes a bit longer for the heater to warm up but now it doesn't at all so I'm guessing that the thermostat is stuck. The entire cooling system was replace in July of 2019, which seems odd that the stat would go so quick. Is there anything electronic that would cause the engine to not heat up other than a stuck stat? Also, even when the engine temp does finally come up the idle is still hi, but will occasionally drop to 800 to 850, more likely happens if I put it in neutral. This is what makes me think there may be something more than just a low engine temp issue caused by a stuck stat.
Side Bar - I reside in Chandler, AZ and have yet to find a GOOD and honest mechanic/shop, if there is anyone in this area that can recommend one I'd consider sending you a nice bottle.

 

[miesk5]

Yo Rock,
Quickie reply;
P0125 Insufficient Coolant Temperature For Closed Loop Fuel Control "...●Indicates the ECT or CHT sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting engine.
●Insufficient warm up time
Low engine coolant level
●Leaking or stuck open thermostat
Malfunctioning ECT sensor
●Remember to have engine @ Normal Operating Temperature before doing the KOER portion
□
Semi quick tests;
DTC P0125 INDICATES EXCESSIVE TIME TO ENTER CLOSED LOOP FUEL CONTROL
Diagnostic Trouble Code (DTC) P0125 indicates the ECT sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting engine. This DTC will light the MIL.Possible causes:
Insufficient warm up time.

Leaky or stuck open thermostat.

Low coolant.

Check coolant level.

Is the coolant level fill correct?


Yes No
GO to Thermostat Diagnostics located in the Cooling System Group in the Service Manual for further diagnostics.
...
miesk5 Note; See 96 Bronco/F Series Workshop Manual @ http://www.diesel-dave.com/vehic/manual/stj/stjleft.htm
...
FILL to proper level. COMPLETE PCM reset to clear DTCs (REFER to Section 2A, Powertrain Control Module (PCM) Reset). COMPLETE Comprehensive Component Monitor Drive Cycle (REFER to Section 2A, Drive Cycles). RERUN Quick Test.

 

[dbmcd]

Check or clean your AIC (air idle control) valve. It's vacuum operated and gets dirty and sticks causing irregular idle speeds.