2.9 Cold Idle Issue!

My 1991 2.9 auto Ranger has an issue when cold. When cold started, the idle starts at a normal high idle and then after about 1 second of that it drops to a super low idle and dies when put into gear. The only way to get it to go into gear without dying is to hold the throttle to bring the RPMs up and let it warm up for a second and then drive off. Then once warm when you start it the starter will turn the engine really fast as if it is trying to fire up and you have to press the throttle to get it to fire up the rest of the way. Once this is done it is good to go and has normal power. My battery light also comes on intermitantly but my voltage gauge reads normal. I have also replaced the IAC valven with no luck.

I will post a video of the issue later today

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The IAC Valve should open all the way with Key On, that's for maximum air for start up
That's why any fuel injected engine should REV to 1,500+ RPMs on startup

Computer then uses the ECT(engine coolant temp) sensor to set idle levels for cold, med, or warm engine
ECT sensor is not expensive so while it can be tested many just replace it on speculation.

There are TWO temp devices on the engine
ECT sensor used by the computer only, always has 2 wires
and
ECT SENDER, used for the dash board temp gauge, has only 1 wire in 1991

They look similar but sensors use 5volts and sender 12volts so NOT interchangeable

I would replace or test ECT sensor


Battery light should come on if engine RPMs drop too low, say under 600
I would get a Volt meter and test the battery, engine off
12.8v is a new battery
12.5v is a 3 year old battery
12.3v is a 5 year old battery and time to look for a battery sale

12.2v or lower is a failing battery, "click, click, click" is in your future

Start engine
Battery should now read 14.5 Volts or so, above 14volts, but under 15volts

Thats the alternator working, the alternator supplies ALL the voltage for the truck while engine is running, the battery is JUST for starting the engine, after that it is not used
The Battery Light coming on means battery IS being used, and shouldn't be.

That why battery light is on when key is on but engine is off, battery is being used at that time to power the truck

After engine has been running for a few minutes check battery voltage again
Should drop down to below 14volts, 13.5v or so, this is correct, over 14volts long term will "cook" the battery
Now turn on all the lights and heater fan to HIGH, voltage should still be 13.5v or so
If its dropped lower then you have a failed Field in the alternator
There are 3 Fields, if one fails then you lose a third of alternators power capacity.
i.e. dimming head lights at idle is NOT normal, lol

You can run with just 2 fields but I would shop for alternator sale

That clears a lot up for me!

I actually replaced both coolant sensors this past fall when the one for the gauge went out on me. I will have the alternator and battery tested soon. I have a check engine light now and I will check them when I have more time

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