IAC action

[HeavyEX]

When I look at the IAC while it is plugged in, and turn my key to the ON position, the IAC makes a pop sound but doesn't really move the plunger at all. I thought it was supposed to close and then open back up or something...some kind of movement. I bought a new one from Autozone but it does the same thing. Is this what it is supposed to do?

 

[my98nnj]

Does the truck start, run and maintain idle speed correctly?

 

[HeavyEX]

Yeah, seems to run fine. When I unplug the IAC the idle drop is negligible and when I plug it back in it surges for a split second. But I keep getting lean codes and I am running through all the possibilities and I noticed that this IAC never seems to close and the plunger doesn't seem to move...I blocked it off for a night and the codes didn't get thrown again so I thought it might be the IAC...bought a new one but didn't install it because it does the same thing. So I want to know what the IAC on other 5.0's do when the key is turned on.

 

[deweyville65]

It is my understanding the IAC pulsates as needed with control from the computer. In that case, the computer senses no need to regulate the idle speed if the engine is not running. Therefore the IAC will not operate if you have it removed from the engine, and the engine is shut off.
I have not thought about this before, but while you have the IAC off the engine, have someone turn the A/C on and off, see if the IAC moves then. I dont know if it will or not with the engine not running as the computer will not get any other signal to change idle speed.

 

[deweyville65]

If you are getting lean codes, I would be looking for vacuum leaks.

 

[HeavyEX]

I will check out the AC situation as soon as I can. I also blocked off the port the IAC mounts to and started the car with the IAC off but still connected, and the idle dropped significantly but the IAC plunger still wasn't moving. I adjusted the amount of air I let in until it completely died and the IAC still never moved. I don't know, I am sure it probably is a vacuum leak like you said, but it just didn't seem like the IAC was ever doing anything except acting like a vacuum leak since it was always just partially open.

 

[deweyville65]

I had to replace mine recently because I cleaned it with intake leaner. Like yours,mine was partially open. So I decided to clean it. Worked just fine before the bath, wouldn't work at all after. $12.00 at the local U-Pull-It. Learned a lesson there.

 

[HeavyEX]

I cleaned mine too, but it doesn't seem to be doing anything different now. How did you know it stopped working? Did it get stuck closed? was your new one open by default as well? The one I bought stayed open too. My local pick-a-part wanted 20 bucks. Figured it was only 50 for a new one, wish I could get one for 12 bucks, I would swap it out just to see if it helped.

 

[deweyville65]

When mine failed, engine would idle very slow, if at all, A/C would not stay on. I adjusted the throttle butterfly stop screw to keep the engine running and the A/C operating until I got a different IAC. The (new) IAC was also in the open position, just like the one I took off. I don't know how the damn things work, it doesn't make sense to me they would be partially open when removed. But if your engine idles,theA/C works at idle, and the engine RPM increases at cold start, then the IAC isn't the problem.

 

[Joe Dirt]

Just a tip- if you're getting a new IAC, don't even bother with the Duralast IAC. It isn't very Dura, and certainly doesn't last. They're infamous along with the Duralast DPFE's for lasting a few months, sometimes weeks. Some go for a long time, but they're the exception.

Order the Motorcraft from Rockauto, it's $65

http://www.rockauto.com/catalog/moreinfo.php?pk=382800

 

[koda2000]

I don't know exactly how the IAC works (other than it opens/closes based on what the PCM tells it to do), but I would start looking elsewhere for your "lean" problem. Frankly, if the engine idles okay I don't see why you're hung up on the IAC. I think it's much more likely you have a vaccum leak. I'd check all your vac hoses and connections first (don't forget the vac ball in the front of the passenger side fender). If that all checks out, then check the PCV valve hoses and connections. If everything looks good then there's a good chance your intake o-rings are leaking (very common on these engines). The reason the lean code went away when you blocked off the IAC port is that you stopped one source of air getting into the engine, this richens the mixture.

 

[HeavyEX]

Yeah, I think you are right. I will keep looking for vac leaks. I don't know about the ball by the passenger fender, could it just be stuck? I have been through quite a bit of muddy water the last 2 years. I already checked the PCV valve and hoses and used up at least 2 cans of carb cleaner looking for leaks, do you have a tip on how to test the Orings on the intake? I assume you mean the Orings that seal the fuel rail? The last 250 miles it hasn't thrown the code again even though it was throwing it every time I drove it (which wasn't very often). I have been driving it more since I have been trying to figure out what is wrong with it, could the seal on something have swelled back up because of the driving? Other than that I don't know why it would have quite triggering the code.

 

[koda2000]

I didn't see where you say which engine you have (are all EB/AWD's V8's?) but the 4.0L SOHC V6's use o-ring seals for the upper and lower intake manifolds. Vac leaks, because these o-rings shrink w/age, are common on the 4.0's. The 5.0L V8 uses gaskets for the upper and lower intake. It is less common (but not uncommon) for the V8's to develope intake manifold gasket leaks.

If you have the V6, the o-rings will sometimes swell up with heat. if you're driving it more that could be why the codes have stopped, but they'll be back.

 

[HeavyEX]

Sorry, I should have specified, I do have the 5.0. I know about the vac canister below the battery but I still don't know what the vac ball is by the passenger side fender... I will llook for it when I get home.

 

[koda2000]

Sorry, I should have specified, I do have the 5.0. I know about the vac canister below the battery but I still don't know what the vac ball is by the passenger side fender... I will llook for it when I get home.

You can't see the ball w/out removing the passenger side inner fender (or at least taking in lose from the front). It's a reservoir, I don't believe it has any valves associated with it, but there's probably at least one check-valve somewhere in the vacuum line system to keep from losing all the reserve vacuum when the engine is turned off. Sometimes the ball can become damaged or a line can come lose or leak. I guess it's because the ball is hidden that it can get missed while checking for leaks. This is the reservoir that keeps vaccum at the ready to work things like you HVAC controls.

 

[HeavyEX]

OK, I never did take off the inner fender to see the vac ball but I did find a vac line going into the fender well in the area where that ball should be and I put a vac guage on it and it did not lose any vaccuum.

So... here is what I have done so far

I have replaced the intake manifold gaskets and the fuel rail orings.
replaced fuel filter
egr valve
dpfe sensor
egr vac solonoid
pcv valve and all related hoses
cleaned maf sensor and iac valve
blown cigar smoke through the intake with which all I could see smoke coming out of was the iac valve and egr valve

cannot find vac leak...but I am sure there is one somethere because the transmission hesitates to shift when it should sometimes too...the lean codes paired with this symptom lead me to believe it is definitely vacuum related. I check the lines on top of the transmission and they are good. Does the 1999 have a modulator that could be leaking vacuum?

 

[HeavyEX]

I think I have determined that a weak fuel pump was to blame for my lean condition. I spent so much time and energy looking for a vacuum leak which I think was non-existent. I replaced the pump and I think the problem is fixed for now. Thanks for all your help.