I have a 1997 f-250 LD with a 5.4 and have noticed a slight miss to the motor. It now seems to idle around 600 to 700 rpms when in drive with a slight miss to it.I recently changed the plugs with motorcraft and boots, because the motor was at 90,000. I also installed a k&n filter. I took it to ford and they had it all day, had it on the computer and heat tested the motor and they said it was running great.And also said that the truck will cut cylinders or something to save fuel...Dont know if i believe that on my 97...But, does any body have ay ideas?...Maybe i should put the stock filter back in and i think its been about 6 or 8 months since a fuel filter change. Any help would be great or maybe i am just being a little to picky for a 1997 motor.

 

I used to have a slight miss at idle with my 98 5.4. I cleaned the MAF and it has been idling smooth ever since. I disconnected the battery while I was cleaning the MAF. Follow the instructions on this sight.

Rick

 

the map looked pretty clean today, but tommorrow i guess i will shoot some elec. cleaner in it and see what happens.....And if anybody else has another solution feel free to fire away...thanks

 

It seems to me that the rpms are to low while in drive it should be about 1000, to 1200 rpms. when it is in park or nuetral it should be at 750+/- 50 rpms. just my two cents

 

Mine idles at 600-700 in drive and only slightly high in park. You could run some good fuel system cleaner though the gas tank. My MAF looked clean before I cleaned mine. I have had the dealer do some sort of fuel induction cleaning on other vehicles i've owned. I think you can buy a kit and do it yourself.

Rick

 

well, cleaned the MAF toady (and disconnected the battery for 20 min.)and just for good measure put the stock filter back in (although i dont think different filters would cause this)...The result was about the same, maybe a little better but probably wishfull thinking on my part...I guess i will try to flush the fuel system and change the fuel filter tommorrow.....but maybe the MAF is just starting to go bad??? Dont know really but i will try with the fuel system first since its the cheapest.....

 

Also, I have read alot about IAC...maybe this could be going bad???? Any comments on that since my truck does seem to idle at about 600-700 with the miss...I will still change the fuel filter , but just thought it may be the IAC also????

 

How long has it had the rough idle for?
The earlier 5.4s didn't always idle real smoothly but it shouldn't shake bad or anything like that. They dont cut out cylinders to save fuel. A sticking EGR valve can cause a rough idle but usually it will be very rough and stalling. A vacuum leak can cause a rough idle. The common place on these engines is the elbow on the PCV hose at the back of the throttle body. A bad IAC wont cause a rough idle. It can cause a surge at idle or a stall or high or low idle but not a misfire feeling.

 

Racerguy, i noticed it a few weeks ago. I did notice something similiar when i pulled up to a stop light for a couple of months ago, it would only have a slight miss for a couple of seconds then stop. But, now it is a constant miss and the rpms that used to be around 800 -900, are at 600 - 650. I had recently changed the plugs,so thought maybe i messed it up, so when FORD hooked it up to the computer and said everything was running great I was baffled. And, the miss i am experiencing is not a really bad one, just enough that I know something is not right.

 

I might have to check them hoses, since I was moving stuff around when i did the plugs.

 

Might try removing and cleaning out the IAC (Idle Air Control) with some WD_40. Seemed to work for my F150 5.4 and my inlaw's 5.4 Navigator.

 

Noticed today that my idle while in park is 900 and when I shifted to drive with brake on it went down to 600, I could have swore that it was around 1200 in drive. any way just wanted you to know. Anybody else check their idles it this normal for the 4.6 in fords.

 

Ok...still havent figured it out...I did notice that since its getting colder up north here that in the morning when started up for the first time it seems to idle quite nicely...like around 1000-1200 then back down to around 750-900...BUT, when the moter warms up, it goes right back to the usual bad idle/miss...My question is, does the IAC control the idle at cold and warm temps or is there a combination of parts that work when its colder out?

 

Have you already tried putting in a fuel system cleaner?

 

Booberjinx - The IAC controls the air flow at idle regardless if it is cold or warmed up. When the engine is cold, the puter forces it into a higher idle for warm up. So when it gets more gas, the IAC doesn't have to work as much. That is why it is smooth when it is at higher idle. Clean the IAC with carb cleaner then blow it dry with compressed air or a can of air. If it fixes it, then replace it. The clean fix usually only lasts a short time. Also check the wiring harness to make sure there are no breaks in the wiring and you are getting a solid connection.

LanceKilgore - I don't know though where you are getting the 1000RPM idle speeds. I would be cruising down the road at that point. In Park, mine idles around 650-700 and in drive at a stop, about 500. Even when cold it only hits 800.