Rough idle; IAC bad?

[PashRoot]

So I've got a '97 Ford Explorer Sport with a bit of a rough idle problem. Picked it up cheap for $500; it otherwise seems to run fairly well from what I understand. It's yet to stall on me but has gotten pretty close several times at long stop lights and heavy traffic forcing me to rev up a bit.

I just cleaned the throttle butterfly earlier (was pretty gunked up) but there was little change in performance. Next I moved up to the IAC which caught my attention with an obvious crack between it and the 'intake' (Apologies if my terminology is incorrect; I'm far from a mechanic). I pulled it off and immediately noticed there was no gasket on it at all. It wasn't tightened well on the intake either.

Upon further inspection it doesn't look too dirty on the inside but testing the two pins with a multimeter revealed a resistance of 11-13 ohms. Besides the missing gasket causing problems, does the resistance indicate a bad IAC?

 

[DjDom]

Gasket? What engine do you have?

Mine doesn't have a big gasket, just 2 smaller ones right where the two holes meet with the engine.

Try cleaning it with Mass Air Flow Sensor Cleaner.
You can also try cleaning the MAF Sensor itself. That sometimes causes issues.

 

[PashRoot]

SOHC 4.0L V6. There was no gasket between the IAC and intake so there was an air leak the whole time.

I'll be cleaning the MAF sensor next if this falls through; maybe test it by unplugging it first.

Something else I noticed is that the 'plunger' within the IAC is very stiff and almost won't move at all. I've since ordered a new IAC since I need a new gasket anyway.

 

[DjDom]

SOHC 4.0L V6. There was no gasket between the IAC and intake so there was an air leak the whole time.

I'll be cleaning the MAF sensor next if this falls through; maybe test it by unplugging it first.

Something else I noticed is that the 'plunger' within the IAC is very stiff and almost won't move at all. I've since ordered a new IAC since I need a new gasket anyway.

SOHC? You sure it's not a timing chain issue?

 

[PashRoot]

Eh, hopefully not. I don't hear any distinctive rattles or unusual noises other than the sound of a possible air leak around the IAC or within the vacuum lines. Once I'm running at 1k rpms and higher the vehicle has plenty of power; no hesitation in acceleration. It doesn't seem to be too bad on gas either for its age but keep in mind I haven't owned the truck that long.

I'll post an update once the new IAC arrives in the mail hopefully this weekend

 

[PashRoot]

OK, IAC valve has arrived but on a stranger note, the rough idle has smoothed out quite a bit with the warmer weather; relation perhaps? I'm still going to replace it of course but now I have another question: The IAC valve came with 2 identical (afaik) gaskets. Am I advised to double up on them with the installation or use only one?

Also, I believe the engine is actually OHV.. my mistake.

 

[DjDom]

OK, IAC valve has arrived but on a stranger note, the rough idle has smoothed out quite a bit with the warmer weather; relation perhaps? I'm still going to replace it of course but now I have another question: The IAC valve came with 2 identical (afaik) gaskets. Am I advised to double up on them with the installation or use only one?

Also, I believe the engine is actually OHV.. my mistake.

Did you clean the Mass Air Flow sensor?

And, I wouldn't double up the gaskets.. more risk for air leak. And, do you mind showing me what gasket you're talking about?

 

[PashRoot]

Did you clean the Mass Air Flow sensor?

And, I wouldn't double up the gaskets.. more risk for air leak. And, do you mind showing me what gasket you're talking about?

Haven't gotten around to it yet but I will.

And certainly not

 

[PashRoot]

Well, I can't say I'm too happy. Installed the new IAC with gasket and the idle seems even worse. It'll seem to catch itself just before it hits 400 rpms and boost itself to 1100 or so momentarily. I allowed the computer to reset itself by disconnecting the battery and turning on the headlights to discharge any residual charge left in the system as well.

I also still hear some sort of hissing sound in the front but I can't quite describe it. Vacuum leak perhaps?

I'm also going to take a look at the MAF when the rain stops.

 

[swshawaii]

Any coolant loss? Spray carb cleaner around the intake to detect vacuum leaks. GL

http://www.explorerforum.com/forums/showpost.php?p=2487828&postcount=3

 

[PashRoot]

Any coolant loss? Spray carb cleaner around the intake to detect vacuum leaks. GL

http://www.explorerforum.com/forums/showpost.php?p=2487828&postcount=3

Gonna try that too.

I tried to get some pics of the MAF but my Sony camera refused to focus on the diodes. They didn't look dirty to my eyes (No signs of dust or dirt particles; almost looks new) but one of the diodes was darker than the other.. so maybe they're dirty anyway?

After that I wiggled all the vacuum lines I could find; most of them seemed all really tight and didn't show any immediate signs of stress except for one...

The green one. Felt pretty loose but not like it's about to fall off either. I wiggled it around a bit and felt some of the green brittle plastic come off.

What do these vac lines go to? This is under the battery btw.

(Apologies if I sound ignorant; my expertise is with computers.. definitely not cars, lol.)

Here's a video of how the truck sounds, take note of the loud hissing.

http://www.youtube.com/watch?v=5Ju2uHvfobg

On the note of coolant loss, yes there is a small leak in the radiator but I'm getting a new one installed in a few weeks. Horn doesn't work either but I think the wires are corroded/rusted away to it (or it's dead) as there's a relay click when I press on it. No A/C either but that's not a big deal to me for now.

I just want the rough idle gone so I don't feel dangerous on the highway

 

[PashRoot]

Thinking the computer hadn't adjusted to the new IAC I let it run idle for a good 10-15 minutes or so. Seemed to be doing well after a few minutes so I continued. Turn on the lights, fan circulation, etc. to push the alternator; the RPMs held steady. All seemed good until I gave it a little bit of gas after it reached 800 rpm. It went up then right back down to 500 rpm. Argh.

I also noticed a rich smell of gas in the exhaust.

EDIT: Unplugging MAF yielded no change in rough idle, just a ton of hesitation in acceleration.

 

[PashRoot]

Sprayed for vac. leaks, idle went way up if I sprayed around or near the IAC, which is odd since both the gasket and IAC are new. Took it off and it was indeed sucking in the WD-40 I sprayed around it.

It still doesn't explain the loud hissing noise or where it's coming from though. Not sure what to do at this point and I certainly can't afford a trip to the shop.. I work part time at $8/hr. Hm.

EDIT: Sprayed once more around the intake manifold; the idle seems to only increase on the driver's side. No change in idle spraying the passenger side.

 

[SoNic67]

Loud hissing is from the vacuum getting inside IAC valve via a small gap.
Look at the little black "hat" on it - it is a connection to outside air and sometimes is defective (even "new").

 

[PashRoot]

Wiggled the hoses a bit and tried to tighten them, tightened up the intake, looked left and right for leaks and found nothing.. yet I can hear it. The noise doesn't seem to be coming from the IAC but somewhere within the intake or under the battery. I haven't a clue.

The issue seems to be getting worse every time I drive it. It now stalls almost every time I put it into gear, along with a really bad rough idle. Was going to pick up a pizza and now it's being delivered instead.

Since I only paid $500 for it I'm not too upset but I'm also wondering if I'm ever going to figure out what the heck went wrong. I'm having dad stop by tomorrow to see if we can figure out what the deal is. I only work part time so spending $300+ at an auto shop is still out of the question.

If I can't solve this problem within the next few months I'm probably going to sell it. =\ Definitely not driving it around the way it is right now.

 

[toypaseo]

Maybe look into replacing the DPFE, and the hoses. According to my ex-Ford mechanic neighbor, the hoses themselves are not just basic hose you can buy in bulk from the parts store, but rather silicone based.

 

[koda2000]

there's a vacuum hose that runs from the evap canister, located in the rear, to the purge valve, which is located under the battery. then there's another hose that goes up to the intake. maybe you have a leak or split hose in this area. another poster found a split in one of his hoses just yesterday.

read "What else could go wrong? Loud sound"

 

[PashRoot]

there's a vacuum hose that runs from the evap canister, located in the rear, to the purge valve, which is located under the battery. then there's another hose that goes up to the intake. maybe you have a leak or split hose in this area. another poster found a split in one of his hoses just yesterday.

read "What else could go wrong? Loud sound"

Yeah, that's one of the hoses I've really been eyeing for leaks. It leaves a chalky residue on my hands and feels looser than any of the other hoses but its pretty tight at the connections themselves. Would I be able to safely and temporarily cap off this hose at the intake/TB?

The 'sucking' noise is distinct and easily heard in the cabin with the windows down/doors open on the driver's side but when I try to listen out for it under the hood it gets 'mixed in' with the rest of the normal engine noise, that's where I get lost.

It really seemed like tightening/wiggling the hoses though made things a whole lot worse. Really hoping I didn't break something else.

I might try getting a smoke test done too; I've heard that's a pretty good way to find leaks.

A bit OT, but is the horn right next to the canister? Doesn't work on my explorer and it looks really rusty around there.

I'll keep you guys posted.

 

[koda2000]

i don't think temporarily disconnecting and capping off the questionable hose would hurt anything. i think these hoses have an o-ring (or seal) inside them. that's why they don't feel like they're particularly tight.

 

[PashRoot]

i don't think temporarily disconnecting and capping off the questionable hose would hurt anything. i think these hoses have an o-ring (or seal) inside them. that's why they don't feel like they're particularly tight.

Ah, ok then. Well, I'm about to head out and start capping off some of these hoses in hopes of finding the leak but before I think I'm delusional, does this hissing in this video sound like a vac. leak to anyone? a big one?

http://www.youtube.com/watch?v=5Ju2uHvfobg