Hi everyone, thanks in advance for any leads on this.

Here's what's happening. On initial cold start, the Ranger fires right up. The computer opens up the IAC, Ranger revs to 1500 rpm, then throttles it back over the next 20 seconds until I'm idling perfectly at 750 or so.

When I turn off the engine though, and try to restart before the engine has cooled, it seems that the IAC stays closed and the engine starts rough, staying at low RPM and threatening to die. It usually doesn't die though, and will stutter for a few seconds before idling up.

I did clean up the IAC but it didn't appear to help. It seems like it is technically doing what it is suppose to do, but I don't like these hard starts when the engine is warm.

Any advice?

 

Welcome to the forum

Assuming a 1989 to 2001 Ranger with Lima 4cyl engine, 12 year range

Specific year would be helpful, because they did change quite a bit in 1995 with new computer model

After engine is warmed up pull off IAC Valve and turn on the key, it should open all the way, cold or warm, with key on engine off.
IAC's 2 wires should show battery voltage, 12volts, with key on, the + wire has 12volts all the time with key on, the computer pulses the Ground wire to lower the voltage and close the valve bit by bit, should read about 8volts after startup, but varies by year

If you open the throttle, give engine more air, does it start?
Thats all the IAC Valve does, it gives engine more air

Fuel injected engines don't have a "gas pedal", they have an "air pedal"
In the old days with carbs when you stepped on the "gas pedal" it actually squirted extra gasoline into the engine, so a "gas" pedal

With fuel injection you are just opening the throttle plate, adding extra "air", computer controls the fuel flow, based on air flow

On some years the Spark system could be effected by heat, causing no or slow starts after engine was warmed up.

 

Thanks Ron D,

Just wanted to follow-up. I went ahead and replaced the IAC after I couldn't get it to open. It has definitely helped the engine start up. I was just driving it around for the first time since replacing IAC and resetting computer. I was in stop and go traffic and noticed that the idle RPM would hover between 600 and 900, not stay perfectly at 750 as it did before. I'm thinking this is because I reset the computer and I just need to drive it more. I'll keep an eye on it.

Our Ranger is a 2005, 2.3L

 

2005 2.3l is a Duratec engine, no relation to the Lima 2.3l

Yes, computer will need 2 or 3 "drive cycles" to maintain steady idle with new IAC Valve
A drive cycle is one heat up and cool down
So driven for at least 10 minutes(full 190degF warm up) and then cool down for at least an hour(coolant temp under 120degF)

 

Thanks again Ron D!

The idle is mostly back to normal, but it will still drop down to 600rpm for a second or two when stopped. This probably happens every other time I'm stopped at a light. I'm not too worried about it now, but if I could fix it completely that would be nice.

Here's what the RPM's look like at idle... it does this maybe once per minute at every other stop light.

https://www.youtube.com/watch?v=03gw...ature=youtu.be

 

If possible test battery voltage after engine is warmed up and before shutting off the engine.
Let it idle and watch voltage at battery, expected is 13.6v or so, should be stable

See if the voltage drops BEFORE the idle stumbles, it will probably drop WITH lower RPMs, just wondering if lower voltage is causing the stumble.

Voltage is what holds the IAC valve open and keeps fuel pressure stable
So a drop in voltage would effect both momentarily, until computer corrected for it