Hey everyone.

I have been trying to do some online research to figure out what my issue is for a while and no one ever seems to have the same type of problem.

Let me start out by saying I have a 99 explorer 4.0 sohc 4x4 auto.

I have replaced plugs, wires, air filter, fuel filter, have cleaned throttle body, IAC, MAF, and have tried injector cleaner.

So now on to the issue. Every time I start it, idle will rev up to about 1800-2000 rpms. Then starts it's decline to normal idle. But instead of holding a normal idle at 800-1000 rpms it drops to 100rpms and either dims all the lights or stalls completely. Before it stalls I always just burp the gas and she is fine. I have no lack of power, I can sit in gear at a red light all day, no matter what I do she will never stall out unless I just start her....

Someone please help me figure this dang thing out before I call it quits and have to pay shop prices

 

Computer will open IAC valve all the way for starting, so engine should rev up above 1,500 every time you start the engine, hot or cold.

After startup computer will check the Coolant temp, ECT sensor.
If temp is below 130degF then computer will maintain higher idle, about 1,100
As coolant warms up idle will slow drop to "target idle", automatics usually have 750 target, manual 625

If engine is cold but computer "thinks" it is warm because of faulty ECT sensor then idle would drop down too low and engine would stall.
A cold engine, even fuel injected, still needs to be "choked" or it will stall, "choke" requires high idle, Rich fuel mix and advanced spark timing, no Choke Plate is needed since computer can do all that, but computer needs to know temp of coolant/engine in order to do that

ECT sensor is only about $8 so worth changing.
Fuel injected engines have TWO temp devices
ECT sensor, used only by the computer
Temp SENDER, used only by the dash board temp gauge

Make sure you get and change the Sensor