Rough Idle, cleaning IAC?

[unioncreek]

My 98 4.0 SOHC has has had the surging idle for the last week. Cleaned the IAC today and it idles much better, but it should like a car horn. Does it need more cleaning or replace it?

Bob

 

[J_C]

lol, no matter how many times I read it, "but it should like a car horn" makes no sense to me.

When I clean my IAC, I also stand it up on end with the solenoid end down, put a drop of light oil on the shaft at the bushing and work the plunger back and forth a little to work it into the bushing, then leave it propped up so gravity seeps more oil down into the bushing for a few hours.

If your idle is still a bit rough, one possibility is the IAC is not moving smoothly. Another is the bushing is too far worn out. Another is you've already gotten all the improvement you're going to get out of the IAC and there is some other issue.

So, you could try lubing it, or you could try replacing it, or you could look at other things like hook up a scan tool and look at your long term fuel trims which should be near zero or at least not a high single digit number for more than brief moments.

For what it's worth, when my IAC gets too dirty I first notice the issue when the A/C compressor cycles on at idle, that this lugs the engine down to lower RPM.

 

[unioncreek]

Sounding like a car horn is probably overstating it, but it's what I saw on the forum. I'm going to put a little oil on it. I noticed when I moved it with a screw driver that it didn't move easily. Thanks for the info.

Bob

 

[swshawaii]

If you haven't yet, clean the throttle body and MAF sensor filaments with the appropriate CRC brand spray cleaners
while there. Probably won't affect your "horn sound" issue, but you will be amazed how much better the engine runs. GL .

 

[unioncreek]

I cleaned the MAF and throttle body when I cleaned the IAC. The Explorer was owned by the county and sat for the last two years, so it needs a little TLC. Bought it so my daughter has something with 4X4 to drive when it snows.

 

[swshawaii]

Hope you completely drained the two year old gas and refilled. If not, could be contributing to your idle problem.

 

[unioncreek]

Drained the gas and changed all fluids, it needed a new fuel pump. Runs good. I put some light oil on the shaft of the IAC and moved it a few times. Re-installed it and idles good now.

Bob

 

[RickOTR]

YFI, there's a small filter inside the black cap on the IAC that gets dirty after all those years of service. Pull it off and take a small pick and separate the two halves from each other. Once apart, ditch the filter and insert a piece of cotton in it's place. This should take care of the horn noise, or what others have called a Howling sound.

 

[GrayGhost96]

I had a similar problem i would say it sounded like a fog horn, in my case it was the air intake. Others have had it too, search the forum for :
Fog horn sound
Discussion in 'Under the Hood' started by ejbeach, July 29, 2005.

also see:

 

[koda2000]

Replace the IAC. It's a wear item. Don't waste your time cleaning it or oiling it. If it makes any difference at all it will probably be temporary. It's not an expensive part and it's super easy to change. A bad IAC may make your engine idle too low or too high. It can definitely also make a howling noise, but I've never had an IAC make an engine run rough. There are many reasons for an engine to run rough, even more reasons on the 4.0L SOHC engine. Leaking intake manifold gaskets are probably at the top of the list. Most problems should eventually set the CEL. Cleaning the MAF, throttle body and replacing the PCV (and it's related hoses and elbows) are a good place to start. Also plugs, plug wires and fuel filters need to be replaced periodically, then you need to consider leaking fuel injector adaptors and seals.

 

[GrayGhost96]

yes check for leaks in your pcv hoses. had my v8 continental barely running due to a hole in the pcv 90° boot. as for intake manifold, getting a tank of propane and unlit, open the valve and run it around your intake. if the engine races you have a leaking intake gasket.

if it is intake gaskets it's not a hard job. just be careful as the intake is plastic. the torque wrench is your friend, don't overtighten.

 

[J_C]

Replace the IAC. It's a wear item. Don't waste your time cleaning it or oiling it. If it makes any difference at all it will probably be temporary. It's not an expensive part and it's super easy to change. A bad IAC may make your engine idle too low or too high. It can definitely also make a howling noise, but I've never had an IAC make an engine run rough.

Depends? I got a new IAC, maybe 15 years ago. I swapped it in, let it run its course, then lubed and put the old one back in.

Worked fine for a few more years, then I lubed and put the new/old one back in, so maybe a 3-4 year cycle. I think it's handy to have a 2nd one, but if you keep lubing them at the first sign of a problem, they can keep going.

I didn't get any kind of noises but the (only) symptom I had was rough idle, particularly when the A/C compressor kicked on. There was no noticeable difference above idle.

 

[koda2000]

Depends? I got a new IAC, maybe 15 years ago. I swapped it in, let it run its course, then lubed and put the old one back in.

Worked fine for a few more years, then I lubed and put the new/old one back in, so maybe a 3-4 year cycle. I think it's handy to have a 2nd one, but if you keep lubing them at the first sign of a problem, they can keep going.

I didn't get any kind of noises but the (only) symptom I had was rough idle, particularly when the A/C compressor kicked on. There was no noticeable difference above idle.

I'd had to replace 2 or 3 IAC's on my 4 V8's over the years. Every one of them started howling or humming, with no other symptoms. One really loudly. Cleaning them did nothing. I don't bother cleaning them any more. The last one I replaced (last summer) was howling at idle and I replaced it with a cheap one I bought on Amazon. Using some points I had on my Amazon card it only cost me just a few dollars (Chinese I imagine). It got rid of the howl, but idled a bit too high. Looking at it I noticed it had a small black plastic hex screw on it's end. Turning the screw allowed me to put my warm idle speed right where I like it (around an indicated 600 RPM). it's been working perfectly since I adjusted it and the howling is gone. Understanding the way the IAC works I don't really see how it could cause a rough idle, but who knows.

 

[donalds]

This iac on a shoc don't Howell or make any noise at all and can be cleaned
The iac on a v8 can Howell and can't be cleaned

Only difference is the v8 iac has a filter

My iac is the original from 99 I cleaned it once I even bought a new one haven't used it I now have a spare
If your engine bay in a shoc Howells likely a vacuum leak
Intake o rings .. vacuum lines evap line etc...


Just my experience

 

[J_C]

^ If by filter you mean that little black cap with the felt under it, my original on the SOHC had one and the OEM replacement I bought from a dealer did too.

It can cause a rough idle because that's it's purpose, idle air control. If the engine needs more air than that flowing past the throttle plate can allow, isn't it supposed to open and provide that?

Maybe I had needed to clean my throttle body too but when I put the new OEM IAC on it cleared up my issue (RPM dropping too low when A/C compressor kicked on) and it didn't need adjustment, don't even remember if it has the adjustment like Koda's aftermarket IAC does.

Mine did not howl, though I don't know if it might have started doing that if I had left it on longer. Now that I recognize the issue and benefit to swap in my other cleaned & lubed IAC, it never gets as bad as it did the first time.

 

[donalds]

^ If by filter you mean that little black cap with the felt under it, my original on the SOHC had one and the OEM replacement I bought from a dealer did too.

It can cause a rough idle because that's it's purpose, idle air control. If the engine needs more air than that flowing past the throttle plate can allow, isn't it supposed to open and provide that?

Maybe I had needed to clean my throttle body too but when I put the new OEM IAC on it cleared up my issue (RPM dropping too low when A/C compressor kicked on) and it didn't need adjustment, don't even remember if it has the adjustment like Koda's aftermarket IAC does.

Mine did not howl, though I don't know if it might have started doing that if I had left it on longer. Now that I recognize the issue and benefit to swap in my other cleaned & lubed IAC, it never gets as bad as it did the first time.

Hmmm that's interesting I never seen a shoc with a filter even the replacement ....China...
I've only seen the filter on a v8
Thanks for the correction

 

[2001SportOwner]

that vacuum elbow is a common cause to check out, under the radiator hose, move it and you will see it

 

[swshawaii]

^ Notorious PCV elbow is a very common issue with the "Job 2" SOHC engine. It's even a sticky on the ST sub forum.
http://www.explorerforum.com/forums...171-p0174-4-0l-sohcs-sport-sport-trac.314670/

@2001SportOwner should bookmark this IF you have the Job 2 engine with the oil fill on the passenger side.
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