I have 1998 Expedition that has a high idle problem for several years ! I can disconnect the battery and the idle will go back down for several days ! now it has gotten worse ! When correct the RPM is 700 in neutral and 650 in gear ! hardly any change. Then the idle goes up and down after a minute or so .
I have repl idle air control valve with no luck ! Local Ford dealer found a bad hose, the one that is hidden off the bottom of the iac. It has not had the intermittent rough idle since ! It still has the up and down idle problem of 1100 in neutral and 900 in gear ! The Ford dealership said should be around 650 in gear and when working right it is ! I drove the truck home from the ford service and it was fine ! Next morning at start up RPM does not come down where it should and has this large swing in RPM from neutral to drive as described above. The truck has95000 miles on it. I have had the transmission fluid pan cleaned and repl. Repl AC comp that was leaking oil at the front , brakes and tires I am planning on keeping the truck . I had the dealer to repl the plugs last week 5000 miles short of the recommended 100,000. The idle is erratic, I can watch the RPM go up and down whie sitting in my carport. I am a TV Tech and need some help . My dealership said bring in and leave overnight so can check cold, but I don't know what he will find ! he thinks may be another hose leaking ! Any one had this or any help appreciated !!!

 

Welcome to the site !

This thread will probably be moved to the proper forum.

The Expedition forum

https://www.ford-trucks.com/forums/s...d.php?t=300691

 

I have experienced in the past and was experiencing a similar problem recently. I cleaned my Mass Airflow Sensor and my throttle body (inside and out) and the problem has gone away.

 

look for an air leak on the intake (use carb cleaner to spray around base of intake etc. and look for an idle increase)

also look for an exhaust leak. This will cause the ecu to adjust the idle as it thinks it is too lean then rich...

 

did any of this help your problem, i have the same issue. my email is wjoliver@sbcglobal.net let me know what cured yours. i replaced my IAC and it helped for a bit, now prob is back, exactly as you describe

 

It has gotten better now that the weather is cool ! The idle came up today when I stopped at a light . I turned the key off and restarted the engine and idle camme right down to normal ! If I can recall it has always been worse in the hot summer months !!

 

now --- ive done my iac and sprayed for leaks aroung the intake, and cleaned the throttle body and exterior of the throttle body, and my idle is UP!!! even higher. 80k on the truck, and its a clean rig, i need help!

 

I've got this same problem on my '98 4.6. Was pinging badly and cleaned the maf and fixed the pinging but the high idle is still there. Sometimes will idle at 2500 rpm and when I turn key off and restart it it works normal. Could not find any leaks so I guess I will change the IAC valve, although in these threads it doesn't sound like that is the problem. Any one else have any suggestions?

 

IAC,That did not help me at all ! From what I have heard that causes low idle or won't stay running ! I said mine had gotten better with the cooler weather ! It has started again , intermittent as always. I noticed it has gone up from the 1200 RPM at times !
Taking the batt cable off will fix it temporaily . I have 100,000 on mine now ,so I guess I can live with it ! It is a pain and no one can give me an answer as to what it is !
If you find anything I want to know ! I will post if I do !!

 

OK GUYS I HAVE THE FIX! the hose that connects from the valve cover to the intake (im quoting the mechanic as best i can) and the valve that is in between there somewhere were clogged, forcing air to back flow into or out of the intake making the enging think it needed to idle up. thats the fix, and no probs since. i cant find my bill to describe the exact part. but it made sense. hope that helps.

 

thanks, will check that

 

Are you talking about the PCV valve here?

 

...Welcome seg to Ford Truck Enthusiasts!

We are happy you have chosen the best source for Fords.

Enjoy FTE....and
JOIN CLUB FTE -SUPPORT THE FORUMS!
…..See you on the boards.

 

I carried it to a guy that used to work for a Ford Dealership for many years and is good on Lincoln Mercury and Ford ! He replaced the TP Sensor and I think it is fixed ! Just picked it up Today April 30, 2006. I will post back in a couple of weeks and follow up ! It stays at 650 RPM now in gear and changes hardly at all in neutral ! It always was worse in warmer weather ! Having a cool spell in north Mississippi now but I feel good about it this time. This is the throttle position sensor !

 

I replaced my PCV Valve and my idle evened out ! Before that it would fluctuate slightly! Maybe you should try replacing that! Good Luck!!

!!