I hope this is the best sub-forum to post this in. I've taken her in to my mechanic twice now, yet these issues are still persisting. For a while, I had been noticing occasional, long cranks before starting, but it would always start. I also had an issue with the idle fluctuating between ~750rpm (normal idle) and ~500rpm while sitting at lights (it would suddenly "dip" to 500 and right back up, accompanied by a loud "click" sound at about 5-6 second intervals, completely at random).

A few weeks back, I had some trouble starting it--this time it sounded like the starter wasn't getting enough power. I had to press the gas pedal slightly while cranking to get it started, and the rpms were fluctuating wildly after the start, going up and down (down so low I thought it was going to stall). After taking it in, they said the starter was pulling 300 amps and needed to be replaced along with the battery and idle air control valve (they also cleaned the throttle body). So I had all that work done, and I'm still experiencing long cranks and idle fluctuation. I also was now hearing a very high-pitch whistling sound (almost like a dog whistle) around 2000 rpm, more noticeable when going up hill and in higher gears.

So I took it back and they swapped out the idle air control valve again in case it was a bad one, but nothing changed.

Although both issues are not as "severe" as they were before I had these parts replaced, they are still present. I actually had one crank that lasted about 5 entire seconds before the engine fired up. The engine shakes violently when these long cranks occur too. The long cranks always seem to happen in the afternoon, but the idling fluctuation happens at various times.

Since the shop said they couldn't reproduce the idling and cranking issues, I started to record my tach and every startup until I caught some footage. Here are three videos demonstrating these problems. On the first video, the idle fluctuates at 0:06, 1:51, and 2:01. The high-pitch whistling sound doesn't record well, so no video for that, but it's definitely there all the time. Any thoughts on what could be going on? Btw, the AC was not on when these issues occurred.

Idle Issue:



Crank Issue:

 

Welcome to the forum

Automatic or manual transmission?
EDIT: I see in the video an automatic shifter


On all engines RPM is control by air flow not gasoline flow, if you add more gas engine floods, less gas engine pings/knocks, but RPMs remain the same.

The IAC(idle air control) Valve is used to by-pass the throttle plate, IAC valve passes air coming thru MAF sensor not from outside the intake, because all air coming into the engine needs to be monitored with a MAF(mass air flow) system.

The whistling sound comment certainly reads like an air leak.
(side note, on the IAC Valve is a black cap that allows pressure to escape so valve can move in and out, if valve seal is not sealing well then you can get a whistling noise from under that cap, new or not, cap just pulls/pops off, there is a small filter under it, you can drive without that cap inplace to see if noise gets louder.
Pictures here: http://www.explorerforum.com/forums/...-w-pics.84220/
And this would be a vacuum leak.)

The computer operates the IAC Valve to maintain a target idle, based on engine temp.
Colder engine higher idle.
On start up(without touching gas pedal) the computer will have IAC Valve opened all the way, so RPMs should go high, then drop as computer closes IAC valve slowly to set engine temp based target idle.
If there is an air leak, vacuum leak, then computer would try to maintain the target idle while air flow was constantly changing, so you get fluctuating idle, computer is pretty good at maintaining a specific RPM within 15rpm of target, but that also means it can fluctuate alot with even a small vacuum leak, lol, its to precise for it's own good

Easy way to test for an air leak is to warm up engine to normal operating temp then let it idle.
Unplug the wires on the IAC valve, IAC Valve will close and idle should drop to 500 or engine may even stall, either is good it means no air leaks.

If idle stays at 700 or higher you have a leak.

The 4.0l SOHC engines had a common issue with PCV Valve hoses cracking at the elbows, on the underside where it would rub and it would be missed on normal inspections.
And the PCV system is, in general, a common vacuum leak source.
Move these(and other vacuum) hoses around while engine is idling, see if idle changes from a cracked hose being moved.

 

Thanks, Ron. I'm not quite sure I got all of that, but let me try to clarify a bit:

1. It is an automatic (to answer your question)

2. The whistling sound only happens when driving (not when idling) and only around 2000rpm (+/- 250rpm). It goes away above or below that rpm range.

3. They've replaced the IAC twice, so I'd assume they checked the things you mentioned (this is a very reputable shop in town, and the second replacement was on their dime). Regardless, I don't feel comfortable testing it myself.

4. The whistling sound had NOT occurred AT ALL before the IAC was replaced initially, yet I was still experiencing the idle fluctuations.

After some more research, I seem to be leaning towards the AC compressor as the culprit. Apparently, the AC compressor is on even when the fan is turned to defrost or feet/face (combined) setting. My AC has also been taking a long time to get cold for about a year or more now. So I'm thinking the compressor is cycling on and off more frequently due to low refrigerant, and the clicking sound is the compressor switch?

But what about the long crank issue (3rd video)? What could be going on there, especially given that it is so random?

 

Ron, also, my IAC does not look like the one in the link you posted. There is no black cap. See mine below:

 

Hey, guys. Unfortunately there has been no improvement in my Ranger's issues, except I did figure out the idle fluctuation cause. For at least a year, my AC has taken a long time to get cold, so I'm guessing low refrigerant or a dying compressor. But after doing some online research, I read the AC compressor runs even when the fan is set to feet/face or defrost (both of which would be the only settings I use besides AC), so apparently the compressor kept starting and shutting off due to whatever the AC problem is, and the RPM dips were when the compressor started.

The whistling sound is driving me crazy. Ron posted a link about a possible fix, but my IAC does not look like the ones in the linked post (there is no valve on the side of it--see the pictures I posted). Ideas?

I've had two more long-crank startups since I last posted. One was super long, and of course I didn't catch it on video (). But here's another from last night. Notice the engine shakes violently when this happens. Any ideas what would cause this? It seems to always happen in the afternoon/evening, never in the morning. So strange...

 

Here's the longest crank I've captured on video yet:

It seems to ONLY do this after the truck has been sitting for a few hours (even up to 8 hours), but NEVER overnight. It fires right up EVERY time first thing in the morning (after sitting for about 15 hours), yet does this (see video) after sitting about 8 hours at work.

ANY ideas whatsoever, guys? I'll be taking it in again (3rd time) to my mechanic next month, but would like some input beforehand.

 

Gas engine needs 4 things to start
It needs to be rotated, starter motor, or pull rope(lawn mower)
Fuel, in the correct air/fuel ratio
Spark, at the correct time
Compression, liquid gasoline won't ignite, yes the Movies get that wrong all the time, lol
Gasoline needs to be heated to a vapor or a spark will not ignite it, that is what the compression is for and why it needs to be above 100psi to get the air/fuel mix warm enough to ignite.

Compression is mechanical so doesn't tend to come and go, i.e. intermittent compression is almost unheard of.
So I would take that off the table.
Starter motor is working and engine is turning so that would be off the table

That leaves spark and fuel.
And best test for those is the 50/50 test
Get a can of Quick Start(ether in a spray can)
After the 8 hours, or what ever, try to start engine, if it doesn't start quickly pop the hood and spray some ether into the intake.
You can do this via air cleaner, Power brake booster hose, PCV hose.
Now try to start engine
If it fires right up then fuel was the reason for the no start
If it doesn't fire right up then spark was the reason
50/50