Rough Idle

[ckabee1]

Hi all,

this is my first post, so please hang with me... I have a 98 Eddie Bauer 5.4 4x4 with 68,000 miles. The truck was purchased four weeks ago as my wifes primary vehicle. We took a trip last week and I noticed a rough idle at the stop lights. Further investigation revealed this rough idle starts only after the engine has reached normal operating temperature and seems to go away once the gas is pressed. Performance does not appear to be affected. Also, is no worse with the A/C on and is not present when in park. It was noticed by everyone in the truck, even those in the third row. It shakes the entire vehicle, although it is not bad, just annoying. And, of course, the 30 day warranty is out (by 3 days). Could this be a bad COP, IAC, PVC valve...? I do not have a check engine light.

I have searched various other post concerning rough idle and nothing else seems to match my particular senario. Any help would be appreciated!

 

[monsta]

I would first suspect the IAC valve. It can be cleaned (search for the procedure) and then go onto the PVC.

A bad COP will usually rear its ugly head under load and not at an idle.

 

[EXMAN]

I have the same problem with my 98. It almost seams like the A/C is engaged when you are sitting in drive at idle. I can't find the proceedure for cleaning the IAC valve. The search engine won't allow words under 4 letters. Can someone point us in the right direction?
Thanks

 

[ckabee1]

Thanks for the info, Monsta. I will try to clean the IAC and see what happens. Would a dirty IAC be evident by fluctuating RPM? My RPM appears steady. Rather than saying rough idle, maybe it's more like a vibration? Exman, does this sound more like what you are experiencing? By the way, the ford truck enthusiast site has a thread re finding and cleaning the IAC.

Thanks.

 

[EXMAN]

RPM is steady. I feel it when it's stopped and in drive with the brake on warm or cold. It's very slight, it feels like something is running, like the A/C, but it's not.

 

[ckabee1]

That's it! It's just as you described, once normal operating temperature has been reached. I read somewhere about an A/C wiring harness shorting out on a bracket or something. Sound familiar? I looked in the engine bay last night and did not see anything that could be the culprit. Oh, well, I guess we keep searching. I'm going to try and clean the MAF this weekend.

 

[EXMAN]

Did you find and clean your IAC? Did it change anything? Where did you hear about the wireing harness shorting out? I will look at mine and let you know if I find anything.

Going to clean the MAF? How do you do that?

You might want to try cleaning your throttle body also. Sometimes they get deposits on the inside and the butterfly valve will not close all the way therefore causing a rough idle. Use throttle body cleaner and a rag to clean inside it. Spray the cleaner on the rag not in the throttle body itself. Open the valve all the way to get the area where the valve seats. Make sure you don't get any of the gunk past the valve. I think this is the correct procedure. I've done it on other cars and it worked just fine.

 

[ckabee1]

No, I have not cleaned the IAC. I have moved that down on the possiblities list, because from what I have read it does not sound related to my problem. However, I read yesterday that condensation from the AC condenser may drip on the o2 sensor, causing a rough idle. This makes more sense in that my problem occurs after the engine has warmed up. Even though it happens with AC on or off, I think the condenser runs all the time (poss producing condensation?). I have not checked it out yet, though. Fordf150.net/howto/ has a section on how to clean MAF, throttle body, and IAC. I may try to tackle some of that this weekend.

 

[ckabee1]

Well, I cleaned the throttle body and looked at the MAF. I didn't clean the MAF since it looked brand new. Cleaning the tb did not seem to help. I did not see where condensation could be dripping on the O2 sensor. I will try and get to the IAC this week, but I not looking for any change. I'm stumped! Any more suggestions?

 

[SeaLion]

I have the same issue on a 2004 5.4 with 19,000 miles. At idle, in drive, foot on brake, there is a vibration you can feel in the whole vehicle. No rpm fluctuation at all but a very noticeable slight vibration. Could it have something to do with the Advance Trak feature? Anyone found a cause or cure?

 

[SeaLion]

Update. I just noticed that if you turn the steering wheel slightly when stopped, it makes the vibration disappear. Could it be the power steering? Whoever else has this vibration, try to move the wheel and see if it goes away on yours too.

 

[parkrw]

My dad had a F-150 w/ the 5.4L engine. He called me and told me that his truck was idling rough. We started troubleshooting the idle ctrl valve etc... Lots of other things. Come to find out, there was a small vacuum leak at a hose going from the pcv valve, Y'ed off to the back of the intake manifold. At the back of the manifold the hose was cracked with a small enough hole that you couldn't hear the leak. I replaced the hose and that took care of the problem. The truck ran like you described your's. The engine heat made the rubber expand and the hole get big enough to cause the problem. A/C affected this too. I don't know if this will help you. Just an idea.

 

[davrober]

I noticed it too today an an 99 expy I just pucked up this morning. A slight slight vibration but rpm is rock steady. I opened the hood and heard a little hissing noise that slowly subsided Id suggest shutting it off and opening the hood right away and see if you hear the noise I think it may be vacume . Its on the pass side of the engine block somewhere in the middle to rear.

 

[green03]

Not saying that this is the solution to anyone's problem but if the airfilter gets dirty (almost plugged) on these trucks it will idle rough. It starts adding timing (instead of adding more air) to bump up the idle speed and you will notice a shaky idle.
Always check the basics first.....
Matt R