Greetings All

Just purchased a Ranger with 4.0. Seems to talk it a long time to come off cold idle, i.e., 2 minutes on cold idle (1500 rpm), another 2 minutes at about 1250 rpm, and then another 30 sec. before it drops to 1000 rpm. Only when at full operational temperature does it drop to 800 rpm. Seems like this is taking longer than it should. Anyone know if this is correct, and if not what sensor is the culprit ?

 

Welcome to the forum

No not normal.
What does the temp gauge on the dash show?

Is it slow to get to operating temp as well?

If so then thermostat could be stuck open.
Easy test is to start cold engine in driveway, pop the hood
Feel upper rad hose, it will be cold of course.
Let engine idle for 2 or 3 minutes and feel it again, should still be cold
If it is warming up with the engine then thermostat is stuck open.

Engine takes 5 to 8 minutes to get coolant in the engine to 195degF(operating temp) depending on outside temp of course, then thermostat will start to open and upper rad hose will start to heat up.

Also when doing the test, pop the hood first and try to spin the rad fan, it shouldn't spin, it will move but not after you let go of it.
Start it and let engine run for 20-30 seconds then shut it off.
Spin the rad fan, it should spin easily, you are checking if fan clutch is stuck on full engage, this keeps engine from warming up as fast as it should.

ECT(engine coolant temp) sensor reports coolant temp in the thermostat housing to the computer, computer bases idle RPMs on the reported temp.

Good how to here on thermostat housing and sensors: How To Replace the Upper and Lower Thermostat Housing on a Ford 4.0L V6 SOHC Engine

2004 may only have 1 ECT sensor, earlier had ECT sensor AND ECT sender next to each other on the housing, sender was used for the dash board gauge only, in the mid-2000's Ford switched to just the 1 sensor and computer controlled the dash temp gauge.

 

Excellent info Ron, thanks for the reply.

I will check all of the items you have identified.

As far as the temp gauge goes I have not watched to see how fast it climes. I can tell you when the engine is warm the temp gauge is sightly below the half way mark.

I will time how long it takes for the temp gauge to reach the half way mark, and reply to see what your thoughts are at that time.

Thanks
Chris