98 Expy has rough idle after warm

Hi,

My 98 5.4L has rough idle after it warms up just a few minutes.

Idles and starts fine when cold but very rough when warm.

I've checked all lines and all seem to be intact after a check engine light which was caused by a bad vacuum line from the pcv valve assembly.

I fixed that and as far as I know, no ore vacuum leaks.
Also, since that repair I have not had a check engine light in over 1,000 miles.

I'd love to loose the rough idle however.
I've replaced the IAC valve as well as the EGR valve.

I have not replaced any plugs but I have them.

I have tried (SeaFoam) for injector cleaning but no positive results.

The vehicle runs perfect and gets the average 13 MPG and starts and idles very well when cold.

I've also put the original AIC valve back on and the problem remains.

Anyone have any ideas as to what I should try next?

Could it be valve damage from the missing vacuum hose I found?
It was a large hose and maybe 5/8 inch diameter at the rear of the intake just below the IAC valve.
Who knows how long the previous owner drove it under this condition.

The engine has about 60,000 on it.

Looking for advice!

I just recently started having this problem also. It starts fine when it's cold but after it warms up it idles extremely rough. Mine will rev up to around 1200 rpm for a few seconds when I get home from work and put it in park. Then it will idle back down to normal and then drop to 400-500 rpm and shake as if it's wanting to cut off. I drive 72 miles round trip everyday to work and it never does it while I'm driving. It's only when I'm stopped at a light or idling. My CEL came on and Autozone read it as being a rich fuel mixture. Could this be caused by a vacuum leak or my fuel pump going out? It's odd to me that it only does it when warm.

I just recently started having this problem also. It starts fine when it's cold but after it warms up it idles extremely rough. Mine will rev up to around 1200 rpm for a few seconds when I get home from work and put it in park. Then it will idle back down to normal and then drop to 400-500 rpm and shake as if it's wanting to cut off. I drive 72 miles round trip everyday to work and it never does it while I'm driving. It's only when I'm stopped at a light or idling. My CEL came on and Autozone read it as being a rich fuel mixture. Could this be caused by a vacuum leak or my fuel pump going out? It's odd to me that it only does it when warm.
I never have fixed mine! I bought a code scanner and I do get rich fuel mixture codes every 500 miles or so but then I also get a right or left bank lean code. So I'm confused as it says lean one day and rich another!
My most promising was a code that said excessive EGR flow.
Soon as I saw that I figured that had to be the problem so I put a new EGR valve on.
No change at all.
I've been told that the airflow sensor could be the problem but I priced them and they are expensive and only available at Ford dealers so I have not changed that yet.
I do not have the 1200 rpm rev up at all.
I idle fine at about 700+ but after warm I see idle rpm's at 600 to 650 and then I have the very rough idle.
Mine never gets as low as your 400 to 500.
I only drive 4 miles each way to work but often go to see my buddy which is 25 miles and the thing runs fine on both side roads as well as highway.
Soon as I hit the stop signs or lights though, it idles rough but has never died.
Acceleration from the rough idle is also good.

Your problem could be the idle air control valve.
It is a critical part that could cause your symptoms.

Not hard to change if you have the right tools but I think the part is like $80 or so. So it is not something you would just go buy unless you have the cash to blow.

You say you drive a fair amount of miles to and from work each day, are you sure the engine is still putting out the power it always had while on the journey?
If you floor the pedal on the highway does it still get up and go?
How is your gas mileage now compared to before you had the problem?
Good luck and if you fix it then please post back here in this thread and let me know what it was!

I do have a question, does yours have the air suspension system?
If so then have you had any problems with it?

Mine had it from factory but the original buyer had it removed as it kept going up and down while the vehicle was parked.
So I bought the thing and put the air suspension back in.
Seems to work ok but I hear the compressor running very often which I think is not right.
I did check for leaks and found one at a Y fitting and fixed that but the compressor still seems to run a lot.

Let me know how you make out!

I have not fixed my problem yet but I did find that the vacuum hose going from the PCV valve to back behind the IAC valve has a hole in it. I went to the Ford dealership yesterday and picked up the part ($55) and I'll try to put it on by the end of the weekend. They have two different hoses for the engine (5.4 L). One has a 3/4" end on it and the other has a 5/8" end on it where it connects behind the IAC. Of course mine is the more expensive of the two. The parts are exactly the same other than one end. Mine is the 5/8" and it's $15 more than the 3/4"!!! I don't understand their pricing.

Other than taking the part off the only way to know which one you have is to reach around and feel it. The guy in the parts department said that's one of the most common parts he sells for that engine.
I'll post here to let you know the results.

I have not fixed my problem yet but I did find that the vacuum hose going from the PCV valve to back behind the IAC valve has a hole in it. I went to the Ford dealership yesterday and picked up the part ($55) and I'll try to put it on by the end of the weekend. They have two different hoses for the engine (5.4 L). One has a 3/4" end on it and the other has a 5/8" end on it where it connects behind the IAC. Of course mine is the more expensive of the two. The parts are exactly the same other than one end. Mine is the 5/8" and it's $15 more than the 3/4"!!! I don't understand their pricing.

Other than taking the part off the only way to know which one you have is to reach around and feel it. The guy in the parts department said that's one of the most common parts he sells for that engine.
I'll post here to let you know the results.

I had the same and I think mine was the larger of the two.
I did replace mine but it did not help much.
I was suprised it did not as mine was completely off the intake port.

Let me know your results!
I also do not understand the pricing!
My other parts were fine and I just needed the rubber part that hooked to the port behind the IAC valve but NO!
Ford would only sell a whole assembly.

It was easy to change.
You ever replace the IAC valve?
I did and it was a bit tricky but not too bad.

I'm still looking at putting in new plugs but no way will I give them the $800 or so I was quoted!
That is just ridiculous if you ask me!

I installed the hose assembly and it seems to have fixed my problem. I've driven about 100 miles since I installed it and so far so good. I have not replaced the IAC valve. I am going to pay close attention to how the truck performs for a while but so far I've had no more idling problems.

You might try spraying your vacuum hoses with carb cleaner. That's how I found the source of my leak. You'll know it if you hit the leak because it'll idle fine for a second and then go back to idling rough.

Good luck! I'll post if I run into any more trouble or hear of any more solutions.

I had the same and I think mine was the larger of the two.
I did replace mine but it did not help much.
I was suprised it did not as mine was completely off the intake port.

Let me know your results!
I also do not understand the pricing!
My other parts were fine and I just needed the rubber part that hooked to the port behind the IAC valve but NO!
Ford would only sell a whole assembly.

It was easy to change.
You ever replace the IAC valve?
I did and it was a bit tricky but not too bad.

I'm still looking at putting in new plugs but no way will I give them the $800 or so I was quoted!
That is just ridiculous if you ask me!




Hey if you were really quoted $800 , I would love to do the job , My dealer only charges 3 hours at a maint. rate of $75.00 per hr. plus parts , and thats at a dealer , someone is trying to rip you off .

Any way the pcv lines are a big issue as well as coils going bad , especially #4 cyl as coolant would run down and short the coil to ground causing a misfire. Sounds to me like it could be a coil problem , and you need to get some one with a good reputation do the right diag for you

Hey if you were really quoted $800 , I would love to do the job , My dealer only charges 3 hours at a maint. rate of $75.00 per hr. plus parts , and thats at a dealer , someone is trying to rip you off .

Any way the pcv lines are a big issue as well as coils going bad , especially #4 cyl as coolant would run down and short the coil to ground causing a misfire. Sounds to me like it could be a coil problem , and you need to get some one with a good reputation do the right diag for youI never formally asked for a quote but have seen that amount posted at several sites for this vehicle as well as my head mechanic at our grounds maintenance department did receive a quote but his was nearly $1,000!!

No thanks on the offer as I'm sure I can do this myself!

I just need to dedicate the time and simply do it!

Thanks for the offer however!