I don't know if this applies to automotive engines or not. But my snowmobile had the same exact problem last year. Idled like s**t, but as soon as you would give it just a little throttle, it would clear itself out and run perfect. I found a plug wire that was resting on the top of the motor. Upon further inspection, the wire was half worn through. I replaced that wire and the idle smoothed right out. Maybe you would want to just check all the wires to be sure they are not contacting anything. I'm sure someone else has some automotive experience with this type of problem, and will let both of us know if this could be the problem.

 

Okay to udate my first posting, the 5.4 miss is at idel. The ideal is at 750rpm and you can feel it real bad. But if you get the rpm's adout 1000 or more it settle down, and the tach stay real steady.I tried different octain still the same results. When under a load you can't feel it.

 

Somebody posted (yesterday) that they resolved a similar-sounding complaint by cleaning a sensor -- mentioned that he used brake cleaner instead of carb-cleaner -- do keyword search on 'clean' 'sensor' and 'brake' or 'brake cleaner' -- and you should find it.

 

I'm new to the message board here, so please be patient. If you've got a 5.4 with a rough idle problem, have someone check out the idle air control valve. Mine had an intermittent rough idle problem for several months, mostly when I pulled up to a red light. Then, it began to have starting problems, first cold, then both cold and hot. It finally refused to start for me last week. I had it taken to the dealer who replaced the idle air control valve under warranty. I've had it back for four day now and it seems to run fine now. Hope this helps some of the others who've been experiencing the same problem(s).

------------------
1999 F-150 SWB SuperCab XLT Oxford White, 5.4L Triton, Auto, 3.55 Ltd. Slip, Pendaliner, UWS Xtra-DEEP Toolbox, Yaesu FT-8000R Amateur Radio Transceiver, Larsen NMO-2/70 Antenna.

 

I just fixed that same problem on my 1989 Bronco with a 5.8L and 350k miles. That's right, 350k miles and never rebuilt. Mine was a bunch of little problems that made the engine go berserk. The Oxygen sensor, the TPS, fuel injectors needed cleaning, the PCV valve, and the backside of the throttle plate was all gummed up with crud from the PCV valve being bad.

These dang computer controlled engines are a pain in the butt. Here in Florida, they just got rid of all emissions testing as of July 1. I think I'm gonna go out to the garage and strip all the computer junk off and change to a nice simple intake and Holly carb.

------------------
Boss™

Just Ordered 2001 F-150 Lariat Wht/Slvr medium graphite leather, 4x4, SC, SB, SS, 99L 5.4L, 44E tran, 7700# payload, Class III Tow, 3.73LS, Skids, Capts chairs, 4W disc ABS, shift-on-fly, keyless, HD everything
Planned Mods:
Westin Chromed Stainless Nerf Bars, ARE LS II bed cover, Bedrug™, Gibson Swept Side Cat Back, K&N filter w/airbox mods, Headman headers, Superchip, 3" body lift with at least 33's, alarm/pager/auto start system, stereo system

 

Had the same problem in my 97 F-150 i took the idle air control valve off and it had carbon in it the book says not to clean it but i did! i was careful though and cleaned it with some internal engine cleaner used to clean outboard boat motors cleaned up real good! i put it back on and i havent had a rough idle yet! and that has been two weeks ago also i had a hesitation when i pulled out sometimes this has dissapeared also so far so good.

 

F-trucks:-

Was the idle air control valve very complicated or hard to take off and clean?

------------------
1999 F-150 2WD SWB SuperCab XLT Oxford White, 5.4L Triton, Auto, 3.55 Ltd. Slip, Pendaliner, UWS Xtra-DEEP Toolbox, Yaesu FT-8000R Amateur Radio Transceiver, Larsen NMO-2/70 Antenna.

 

SORRY did'nt get back sooner it is easy removed just remove the 3 10 mm bolts holding the plastic cover over the throttle body and then then remove the 2 bolts there 8mm i think? it took me about 5 min. to remove! when cleaning the valve be sure and keep the round solenoid end that the wire connects to in the up position it has a small rod going up in to the round solenoid and the cleaner will go up in there and destroy it. so hold your finger over the bottom hole and squirt the cleaner in the top hole and let it soak i used a q-tip and swabed it around in the valve anyways today i did get a little rough idle for the first time in a few weeks! it has been running smooth as silk up until today i had just put gas in it right before it did it so i may have got some bad gas? anyways it has got something to do with it and if it gets the rough idle back like before i think i am going to get a new IAC valve i think there about $45.00 for a new one on wrenchhead.com