1997 Ford Explorer starts and stalls when cold
Working on a 1997 Ford Explorer 4.0L SOHC V6 with 58k on it. This vehicle was brought in for a stalling when cold problem. Items that have been replaced are the standard ones i.e. New IAC motor, and new Mass Air Flow sensorand a full tune-up with Motorcraft Platinum plugs, And throttle body was cleaned. Fuel pressure was checked and is 40psi. Have checked for vacuum leaks with a smoke machine, and none have been found. Observed all sensor readings, and all are within acceptable ranges, and no codes have been set.
Here are the symptoms, Start vehicle when cold out, (we live in Pennsylvania, and it is 20 degrees here right now) Idle will flare to 2000rpms, telling me that the IAC is working properly, idle will lower to base idle, engine will begin to shake miss and stall. Re-start, engine will do same thing. Now if you hold the gas at 2000rmps for 45-60 seconds vehicle will run fine and then settle to a nice and comfortable 850rpm idle. None of these problems will re-appear untill the vehicle is allowed to sit for many hours and achieve it's previous cold temprature. Any ideas on this problem would be greatly appricated.