Idle Air Control Valve Issues......HELP!!!

[ChevelleStang]

I have a 2003 with the 4.6l engine. I was having an odd sound (sounded like a thump in the airbox) that I could hear inside the car and a weird idle. So I looked through all the vacuum lines and have not noticed a leak. So I decided to go ahead and replace the IAC valve. So it fixed the odd sound that I was having (I have no idea what was wrong with the other one) but I now have a totally other problem that I think is all related.

The issue now is that when I crank the car (cold) it tachs to about 2,000 rpm and holds and drops a little over about 20 seconds. Once it gets to 1200-1300 rpms, it then starts to rise slowly to about 1800 rpms and then completely drops to 750-800 to normal idle. Its so weird. It does this all in about 30-35 seconds. It was not doing this before I changed the IAC valve. Also, when the car is warm and I crank it, It tachs to 2800-2900 rpms and stays there for about 5-7 seconds and then drops completely very quickly back to normal idle. I cant say for sure that the high idles at start up only happen that way when cold and hot, I think its sometimes random. But majority of the time when starting it falls in the above reference.

Heres the other issue I need help with - this is also happening because of the new IAC. I will be driving down the road and coming to a stop light and the car wont tach down to under 1000 rpm, it will stay at 1500 roughly and will "hard down shift" and wont tach down to a normal sitting idle until the car comes to a complete stop. Literally have to stop fully to bring idle down. Then the car is fine. But it is tough to stop because it is tached up a little and still wanting to pull the car.

Can anyone help me troubleshoot what to look for and do? The old IAC valve had a little rough idle, car shook at idle, and had that weird airbox noise. The new IAC valve fixed the airbox noise but added in a whole new set of issues with high rpms at start up and the high rpm when coming to a stop.

The only odd thing I have noticed is that when taking the hose off the PCV valve, it has a really high amount of suction. I cant say that's a problem but it seems to be much higher than other cars ive worked on. Also the hose that runs from the PCV to the intake looks collapsed on the curve bend that connects to the intake. Almost as if it has to much suction and is closing off the hose. But if I pull the end of the hose off at the pcv valve, it is still pulling plenty of air. Could this be an issue? Is it possible for the system to be sucking too much air?

Also, Mass Air sensor is clean and working properly. New Air Filter installed too.

Sorry guys, im totally lost here. Thanks for helping!

 

[1996EB]

I also have an 03 4.6L. I've replaced the IAC valve on this and prior Explorers. These are evil little devices that if not operating just right, produce multiple issues. I responded to a previous post about IAC issues in this forum, with the following answer (mainly concerning the "thump"). This is the other thread:

http://www.explorerforum.com/forums/showthread.php?t=438009

This was my response in the other post:

My 03 4.6L will sometimes exhibit similar symptoms, but not as severe as yours. I find that if the motor is cold and I start the vehicle and drive off quickly, it will have a slight rev issue when coming to a stop. The best way for me to avoid this is to let the engine "warm-up" for about a minute or two on a cold start. I wait until the RPMs drop to about 800 before putting it in gear. If I don't wait and drive off while the car was idling at anything over 1000 the rev issue will happen when coming to a stop early in the drive. This procedure works for me every time- just wait until your idle drops down to about 800 before driving. I hope this helps.

Additionally, I have a Cold Air Intake (CAI)on mine that has helped my engine breathe better and provided better overall drivability. I don't want to get into the whole debate about CAI (there are a good number of CAI "haters" out there)- it has worked well for me and I'm happy with it.

Getting back to the IAC valve. When I changed an AIC valve on one of my Explorers (don't remember which one), I was very dissatisfied and returned it. the replacement worked better. You may want to think about an exchange on the one that you have now.

 

[lincolnshibuya]

you have 2 issues here, IAC and the elbow hose. Aftermarket IAC is a hit and miss, go with motorcraft (they are cheap online) The elbow that is connected near your IAC is prone to cracking (replace it), it will cause rough idle and a CEL.

 

[apenland01]

And don't forget to reset the PCM when you are done. If you change anything on the intake side (EGR, TB, IAC, ETC), reset the PCM so it will relearn the idle from scratch with your new stuff.

 

[swshawaii]

Surprised no mention of checking for stored trouble codes, CEL or not. Here's the PCV elbow thread:

http://www.explorerforum.com/forums/showthread.php?t=217062&highlight=idle

 

[ChevelleStang]

there was no trouble codes stored. I did reset the PCM so it was all relearned and it did not help.

I have another IAC valve ordered and am picking it up tonight. I will check it out and let you guys know what happens with it.

By the way, thank you all for replying and helping me out.

As for the elbow "being crimped shut" - by this I mean, it looks like there is so much vacuum that it is closing the hose. Do you know why this would be happening? I don't know why this would be?

Im not as worried about the high idle at start up except when it revs to 2800-2900., That is way to high. Im more concerned while im driving and coming to a stop, at random times, it wont tach down and down shifts horribly causing jerking, and hard to actually come to a stop. but as soon as I do actually hit 0 mph, the rpms drop immediately to normal range. Its so odd.

I hope the new one will work. Maybe just the IAC I bought was crappy. It was an aftermarket cheap-o.

 

[swshawaii]

The only odd thing I have noticed is that when taking the hose off the PCV valve, it has a really high amount of suction. I cant say that's a problem but it seems to be much higher than other cars ive worked on. Also the hose that runs from the PCV to the intake looks collapsed on the curve bend that connects to the intake. Almost as if it has to much suction and is closing off the hose. But if I pull the end of the hose off at the pcv valve, it is still pulling plenty of air. Could this be an issue? Is it possible for the system to be sucking too much air?

As for the elbow "being crimped shut" - by this I mean, it looks like there is so much vacuum that it is closing the hose.

PCV valve replaced? Sounds like it's restricted or stuck closed. Don't over tighten, plastic locking tabs easily broken.

http://www.rockauto.com/en/catalog/...pcv+valve,5052?a=Referer+www.google.com+URL+/

 

[ChevelleStang]

PCV valve seemed fine. Took it out and cleaned it but the ball was free and floating around. What are the actual systems of a bad PCV?

 

[swshawaii]

The only odd thing I have noticed is that when taking the hose off the PCV valve, it has a really high amount of suction. I cant say that's a problem but it seems to be much higher than other cars ive worked on. Also the hose that runs from the PCV to the intake looks collapsed on the curve bend that connects to the intake. Almost as if it has to much suction and is closing off the hose. But if I pull the end of the hose off at the pcv valve, it is still pulling plenty of air. Could this be an issue? Is it possible for the system to be sucking too much air?

As for the elbow "being crimped shut" - by this I mean, it looks like there is so much vacuum that it is closing the hose.

Sorry I can't be more help, I find emissions and vacuum issues intimidating. Also dislike throwing parts, but you need to remove and at least inspect the collapsed PCV elbow. Over time, oil and vapors can soften rubber vacuum hoses, even OEM. Certain 4.0 SOHC's have this issue of collapsed PCV elbows but usually throw p0171/174 lean codes. If the elbow feels mushy and soft replace it. Motorcraft KCV-240 (KCV-129) should be the correct replacement but check first. GL.

http://www.rockauto.com/en/catalog/...ion+hose,11784?a=Referer+www.google.com+URL+/

Aftermarket Dorman elbows that "appear" similar. Do a direct comparison.
http://www.dormanproducts.com/itemdetail.aspx?ProductID=68054&SEName=48011

 

[ChevelleStang]

I don't like throwing parts at it either, but im just not smart enough with these issues to figure out how to troubleshoot.

I just bought a new IAC valve again to see if it changed anything and it didn't. So the IAC valve, even though cheap, must be working right. There has to be another issue. Im going to go with a new PCV and hose. The collapsed hose was the only thing that I couldnt figure out. The PCV seems to be fine but im going to replace both and see what result that gives. I will add a message after I do that.

 

[swshawaii]

Replace one at a time. Just curious if either is the culprit. (PCV valve or PCV elbow)

 

[ChevelleStang]

will do

 

[ChevelleStang]

Picked up the pcv valve tonight. Put it on and I change with the car. I took the entire pcv hose off and didn't see any signs of cracking.

Do you guys think it's a bad hose for why it's crimping shut? Or do you think there is another issue?

I really don't want to spend 50 dollars on this hose if it's not a problem.

I'm just lost on what else could be going on. I was thinking tps but it's not throwing a code.

 

[swshawaii]

For testing, temporarily replace the collapsed hose with a piece of 5/8" heater hose. Most AP stores sell it per foot.

 

[swshawaii]

From the OP's eleven page thread linked above. If you read there are many more with the same issue claiming a fix.

As you can see from the attached photos there is obviously a problem. The rubber is deteriorated at the bend and the significant vacuum causes it to collapse. There is a significant sucking sound coming from this point with the engine running.

http://www.explorerforum.com/forums/showpost.php?p=1965554&postcount=11