High Idle 98 Expedition 5.4 L
 

I have 275K miles on my Expedition. I've recently had a rough idle; like panting up and down and sometimes surging. It drives fine. I've read several great threads about causes: dirty TB, dirty MAF sensor, exhaust leak, vacuum leak, dirty IAC. I was going to change the common culprit; the IAC, but on the 98 it's tight quarters even though its 2 bolts and a connection.

Yesterday I looked for a vacuum leak, found none, but doesn't mean it's not there. Changed the PCV valve, and cleaned MAF sensor. I cleaned the mouth and plate of the throttle body while attached with the appropriate cleaner. When I turned it over and brought it up to operating temp, I now have a high idle (1000 to 1200.)

I noticed a seam leak in my muffler. Could this be the problem?

From what I can see, the TB is real dirty. I want to remove the TB and adapter and IAC all at once (4 bolts and vacuum lines etc) and thoroughly clean the TB, change the IAC and inspect the latent vacuum lines.

My question: Is this doable or would you advise not to? Can I take this all out as one unit and work on it on the bench rather than tight quarters or will the fire wall prevent me from removing the bolts?
Are there other possible causes anyone can think of? Any insight would be greatly appreciated.

[/I]Thanks, Kurt kgparry04@yahoo.com

I will patch the seam leak in the muffler.

More often than not, posts with too much information tend to get overlooked. Try to break your post down into questions that are more to the point.

TB removal for cleaning
 

Fair enough, Allro. That's good advice

I guess my main question is if a high or erratic idle can be caused by, among other things, a dirty TB, IAC or MAF, a vacuum leak or exhaust leak, can I remove the TB and the attached Adapter along with the IAC all as one piece to clean them on the bench versus removing them one at a time like the hard to reach IAC?

I have cleaned the throat of the TB, Sprayed the MAF, changed the PCV valve, disconnected the battery for 30 minutes, and did not find a vacuum leak on a cursory inspection (but could be there) and now I have a high idle (i.e. 1000 to 1200)

Thanks for your ideas.

there is a really good post on here that tells you how to remove and re-install the throttle body for the 5.4 but it requires some searching to find it.
i cleand mine a while back but it was a lot easier because i have the 4.6.

here is the link for it

https://www.ford-trucks.com/forums/8...-a-5-4-2v.html

Kermin, I appreciate you taking time to respond.

I see that the 4.6 is more accessible. Did you remove everthing down to the intake? And when you reinstalled it, did you change the gaskets and torque it to spec, or just snug?

I will check that post and report back. Thanks Kurt

Everything you listed can cause a high or erratic idle except for an exhaust leak. Yes you can remove the TB as an assembly to save yourself some headaches.

Thanks again, Allro. One question, should I avoid trying to clean down inside the intake opening or would this be unnecessary?

Awesome thread! I glanced over it before but had little knowledge of the content. Now, with a little better understanding of the system it answered virtually all my questions.

Thanks, again.

yes i removed everything down to the intake but i think you can leave the IAC valve on it .
i replaced the gasked with a new one .
the screws i just tighted them down snug

I would use a vacuum on it while you're there, just in case there is any loose debris laying in there.

Alloro,

The short of my question is, I am in the process of removing the entire TB, Adapter and IAC assembly. My plan was to leave the EGR valve. The left nut came off easy, but the rear bolt (toward the fire wall) does not want to move. I'm afraid of breaking it of rounding it off. Alternatively, I thought just leave the egr attached and loosen the sleeve nut. This one is rusted as well and does not want to budge.

My thought was to use a heavy does of penetrant and let it sit over night and try to move it again in the morning. Any suggestions or tricks that have worked well for you?

My fear is ruining these bolts and then I have a real mess on my hands.

Thanks for your insight.

Kurt

If it were me I'd do everything possible to get the EGR bolt off, even if that means cutting the tube and installing a new one. I say this because if it does break off I'd rather have the intake in my hands rather than installed on the engine to be able to fix the issue. If you have access to an electric or air impact gun you'll be more likely to get it off without breaking it.

Thanks for your insight, Alloro.

The overnight soak and a morning hit with some PB Blaster proved fruitful. While I was able to break the sleeve nut on the exhaust tube, I unfortunately, could not break the two seized bolts holding the EGR to the adapter. I even tried when I got the assembly to the bench to no avail. Rather than break or damgagea nut I shot some TB cleaner inside the EGR and called it good.

I separated the TB from the adapter, and cleaned them both with a combination of pipe-type cleaners, rotory brush and CRC TB cleaner. The TB was absolutely filthy as was the throttle plate, but it all cleaned up beautifully.

While checking the vacuum lines I found a latent vacuum elbow attached to the upper part of the intake plenum between the firewall. I would have never found it without removing the TB and adapter. I'm glad I did cause don't you know it had a subtle crack as did an elbow on the splitter from the pcv valve. I ended up changing all the elbows and soft vacuum lines. I changed out the TB to adapter and adapter to intake gaskets and installed a new IAC with a gasket. (The IAC was remarkably clean.) I torqued everything to spec.

Result: My truck, with 275K miles, has never idled or ran better. I am just thrilled. I would recommend anyone with these issues to undertake this cleaning. It wasn't too bad. I am just a shade tree guy and taking my time it took me about three to four hours. It's hard to say if my issues were all vacuum, IAC or dirt related, but I have peace of mind that it was all done right.

Total cost: About $75.00: IAC $37, gaskets $5.00, TB cleaner and penetrant, $17.00, vacuum elbows and line $18.00.

Thanks to this entire membership for its input.

For the record, before this undertaking, I did not know specifically what a TB, adapter, Plenum, IAC, MAF or vacuum was.