idle RPMs up & down

[Kidd7]

2000 v8 ~200k miles. recently replaced plugs & wires; rebuilt injectors.

This has only happened a few times over the last 2-3 months or so; all after the above repairs. In the morning sitting in the driveway warming up for the day the RPMs go up and down; ~ 500 to 1,500; no change w/ AC, heat, defrost on or off. It only seems to happen when it's cool and damp in the morning. For what it's worth I'm in the Raleigh, NC area, so cool temperature is relative, humidity is usually high.

This RPM up & down lasts for a minute or so and then levels off. To clarify this doesn't happen initially, a few minutes of running normal, then RPMs bounce, then levels out and all good.

Any thoughts on where to start looking?

 

[V8]

Have you looked into your Idle Air Control? That's often the first step in diagnosing engine idle issues.

 

[C420sailor]

What is live data showing?

 

[Kidd7]

I apologize guys I never got an email about replies to this thread. I didn't even think of the IAC, but will check it out. have noticed it's not just idle, when this happens if I press the gas and bring the RPMs up it still does it, bouncing ~1k up/ down. I've not noticed it while driving or after driving, like stopped at a light etc. I recently replaced the Cam position sensor for a different reason and had hoped that was it, but unfortunately not. I tried cleaning around the crank position sensor b/c I do have crud build up there. We'll see how that pans out.

The data, I've not seen anything significant, it hasn't told me anything. I'm going to look it over again though.

 

[Kidd7]

IT recently happened while I was sitting there watching the data. The one thing I noticed is that the vacuum dropped significantly just before the RPMs went up and down.

I tried cleaned the IAC best I could w/o removing it (I don't have a new gasket) and am monitoring. The rough idle did happen after IAC cleaning, but it was significantly less bounce. In the past when this happens the RPMs would swing ~1k up/ down. This last time it was only ~300.

 

[C420sailor]

If you have access to a pick n pull, grab an IAC. Aftermarket ones tend to be hit or miss. Swap it in and see what happens. There aren’t too many things that can cause a sudden, large drop in vacuum that goes away.

 

[amj441]

just unplug the IAC and see if the rpms stabilize. There is a post somewhere on the forum on how to adjust the idle to not stall with the iac disconnected. or just hold the throttle at an idle and see if your rpm fluctuations are there.

Additionally check your live data and look to see what the desired RPM is set to during these times. Check the coolant temperature reading and see if its abnormal in any way. The vehicle may believe its starting to overheat and may try to increase fan speed. since its a clutch fan it will rev the engine up. (this doesnt apply to when you are warming up in the morning but...)

 

[Kidd7]

I'm using torque for live data, not sure how to see the desired RPM.

I did remove the IAC and clean it. It may be completely placebo, but I think the truck ran better.
Will continue to monitor.

 

[J_C]

I'm using torque for live data, not sure how to see the desired RPM.

I did remove the IAC and clean it. It may be completely placebo, but I think the truck ran better.
Will continue to monitor.

Cleaning the IAC can definitely help, IF it's the cause. I also prop mine up on end for a few hours to let a drop of light (~5W-20) oil run down into the shaft bushing.

 

[Kidd7]

I'm adding that to my to do list.
This morning, it's cold~25F; warming her up she started doing the goofy RPM thing again after about 1-2m of running.. I pushed the gas and if I get her to about 1.5K she's smooth, as soon as I let off the gas RPMs up/ down. Finally I shut down let sit for ~30s and restarted and idled fine for another 3m or so. Drove to work w/o issue.
Yesterday morning she's covered in snow and warmed her up for 5-10m no issue.

Did Ford use a windoze based OS in the 2000s? This is following suit: locks up randomly, reboot & fine; I'm just waiting for the blue screen to show up at this point.

 

[fast_dave]

Cleaning the IAC can definitely help, IF it's the cause. I also prop mine up on end for a few hours to let a drop of light (~5W-20) oil run down into the shaft bushing.

View attachment 462091

Just adding to the excellent IAC diagram that @J_C provided;

There is an aspirin size, felt material, AIR FILTER within the Black Plastic Cap that is to the LEFT of the red arrow in the diagram (ABOVE).

Depending on the age of the IAC, over time and environment, that felt pellet can get clogged solid, and make the IAC operate erratically - i.e. Idle Speed Hunting - up/down.

The black plastic cap can be carefully disassembled (from the underside) and you can remove & wash out the felt pellet in warm water.

You can also construct one out of thick felt material (which is what I finally had to do after the original pellet eventually disintegrated from washing).

The filter is necessary to prevent underhood dust from entering the IAC as it pulsated backwards and creates an vacuum inside of it.

Hope that helps!

 

[J_C]

Yeah I clean that filter every once in a while when cleaning the rest. Think it's just a friction fit cap that gets gently pried off - probably better to do this when the plastic isn't cold and brittle.

 

[Kidd7]

Update: I removed and cleaning the IAC again. This time using Q-tips and a brush, got even more crud out. Using needle nose I worked the shaft up/ down and oiled it. Also popped the cap off and used some air to spray off the felt. The cap is metal and with a flat head screwdriver came off pretty easily.

Continuing to monitor. Very hopeful though since improvements have been realized with the prior cleaning.

 

[Kidd7]

In the likes of 'if it ain't one thing, it's another' My wife calls and says it won't start and it's making a horrible noise. I found the starter bolts to be loose, the starter is flopping around and won't engage. I finger tightened them and she started right up. Rinsed off some of the crud down there and gonna get a wrench on those bolts. Thankfully it wasn't anything worse.

 

[Kidd7]

Well driving it today, stopped for coffee. When I start it to head out RPMs up over 1k, drop quickly to about 500 shutter and jump up again. Shut her down for maybe 30s or so. Start her right up idles perfect and runs the rest of the morning just fine.

 

[J_C]

Is it possible that your A/C compressor is on the way out and it's happening when it tries to cycle on?

Then again, I vaguely recall some people have had an IAC that was just too far gone to clean and lube, though I don't know the specifics, seems like it ought to be okay, at least mechanically, if the shaft moves without much resistance besides the spring.

 

[Kidd7]

I thought about the AC compressor also; I have the automatic HVAC and have turned it off when this happens with not change. I'm thinking of ordering a new IAC and trying. I suppose the coil in the IAC could be worn out and the magnetic field compromised.

I know someone on here said after market IAC can be hit or miss, but at this point pulling from a junk yard ain't no better than what I've got.

 

[J_C]

Someone else may remember, but i think the factory Motorcraft IAC is made by Hitachi? I know it was for my '98 4.0L.

If so, this model ABV0048 might be it? The Rock Auto page references it to Motorcraft F67Z9F715AA, F67Z9F715AB, though oddly it is not listed on the IAC listings for a 2000 5.0L:

2000 FORD EXPLORER 5.0L V8 Idle Air Control (IAC) Valve | Shop Now at RockAuto

Fuel & Air Parts and More for Your 2000 FORD EXPLORER at Reliably Low Prices. Fast Online Catalog. DIY-Easy. Your Choice of Quality. Full Manufacturer Warranty.

www.rockauto.com

More Information for HITACHI ABV0048

https://www.amazon.com/Hitachi-ABV0048-Idle-Control-Valve/dp/B00GTHHIJE?tag=seriouexplor-20

*I COULD BE WRONG*, especially about the ABV0048 part #. Online I see it referenced to a 3.0L engine. There's bound to be someone on this forum with a later model year 5.0L that has replaced their IAC and knows the right part #.

 

[C420sailor]

Not sure on the P/N but I believe Hitachi is correct

 

[fast_dave]

@Kidd7

Yes, the factory IAC for the 4.0 OHV was manufactured by Hitachi.

After replacement of the IAC, if your engine is still hunting for correct idle speed, I'd be looking at the age of the TPS.

Reason: Long Term they tend to burn out when the throttle sits forever on one spot of the rheostat inside the TPS (specifically the idle speed spot)

When replacing the TPS, ensure that it's optimized for idle voltage voltage.

From memory, adjust the TPS to achieve a reading of JUST less than 1.0 volts at idle - I think .96 is the sweet spot.

Link 1: 4.0 OHV Absolute Throttle Position

Link 2 (Read this from Page 23 backwards for most recent experiences): adjust your TPS (another free hp mod)