Tommy J

Well, I finally give up on my 2004 FX4 5.4 My low/rough idle has won. I've replaced spark plugs and cops(motorcraft),fuel filter, air filter,refurbed injectors, fpcm,cleaned the Tb off of truck, cleaned the maf, both with appropriate cleaners and finally a new TB which came with a new TBS. Replaced the foam around my air filter housing, checked and rechecked for vac leaks, new vct selonoids. Never has thrown a single code. Swapped new cops around,unplugged cop connections for idle change and on and on. Took it to my mech and nothing. My old mech said TB but new one did'nt make a difference. One said reflash, one said no. Called 2 Ford dealers to confirm over the phone and got the run around about bringing it in for a reflash. Of course they want to do a diagnostic without just giving me a reflash. I've decided to let Ford do a limited diagnostic and a reflash if needed and so help me God it better work. I've tried the relearn and I guess I've freaken done it right. This all started after a spark plug change. It did'nt run so great before the plug change but definately was'nt idling low or rough. Maybe I just woke a sleeping giant by trying to improve this truck. Im hoping I have a story to tell that may help someone when this is all over. Anyone want to bet that its the one thing I did'nt change..................fuel pump. ha ha

Jr817

let me know what you cone up with, ive tried everything and my truck still idles at 500 rpm with no codes

Tommy J

Will do. Did you change your plugs or anything to cause this? My truck is new to me and has 98k on it. I did the plugs and coils as regular maintenance and thats when it all started. It never seemed to have the ***** my 99 5.4 had. everything else I did was to try and remedy this low/rough idle. I guess it could be several other things like fuel pump, fuel rail pressure sensor, bad 02 sensors or just a pcm reflash. I dont think it ever had one but there was a tsb in 05 for low/rough idle and no sticker under the hood. Man, I just hate having to take it to the dealer but I think it may only end up costing me like $150 or so including the reflash.... I hope. i will definately update my outcome. Take care

Jr817

yes i remember like it was yesterday, i changed the sparkplugs and 7 broke on me and went with motocraft original spark plugs and from then untill now ive changed them 3 times, the cops like twice, i never get any codes at all. I changed the timing kit and now it only shakes when its in reverse at slow speeds because the rmp drops really low.... Man i hate these trucks sometimes

Tommy J

Yeah, I open the hood everyday and just stare at the engine bay looking for something i may have missed. I went with MC plugs and cops(not cheap) I guess one could be bad even new. Im taking it in on monday and Im hoping they find something specific. My 99 had over 200k miles on it and ran better with less problems. I'll let you know

jdinner

How does it perform at WOT? My plugged catalytic converters made it shake at idle, run smooth on light acceleration and misfire/pop at WOT.

Jr817

can you post a picture on how you dropped the cat converters? I read your post on another thread, and also how much did you waste on your new cats and did it fix the low rpm?

jdinner

New Catalytic Converters (aftermarket-Walker) direct bolt on were $450 each side. OUCH! Aftermarket Walker WELD-ON are $140.00 each. Since I have been a welder all my life, guess what I chose?

I dropped the exhaust....at the manifold there are two studs on each side. I heated the nuts and removed them. This is forward of the O2 sensors so you will get some codes if you drive for a while like that. I had to use a variety of different sockets on these four nuts as rust had made them different sizes.
It is also wise to run a die up the stud before you start to clean the stud threads.
I ended up getting too busy to weld them on Saturday. I can give more results on Tuesday.
I can tell you that before I dropped the exhaust the mirrors were shaking at idle and now without an exhaust system they do not.

Especial86

iTrader: (1)

Good man!
Just a heads up..
Magnaflow hi flows are $150 for the pair:
Magnaflow 94106 Universal Catalytic Converter (Non CARB compliant) https://www.amazon.com/dp/B000COPC16..._1QX8ub1574FYC
https://www.amazon.com/dp/B000COPC16..._1QX8ub1574FYC

I run these same exact cats up front and that's it.. Deleted the rears in my 04 along time ago.. I'm supercharged and I have no codes at all. I put them on when I was still NA and I did notice a slight milage and bottom end increase.... Slight.

They are obd1 cats so there is a potential to throw a code.. Just drill out 2 spark plug non fowlers and use them to space the rear 02's out of the exhaust stream if you end up throwing a code.
(I did this to ensure no codes, but I probably didn't have to)..
Replace those front 02's while your at it and your truck should be running better than ever..

I had to bend up and flare new flanges at the manifolds, thankfully at my buddies custom exhaust shop. The whole job turned out to be real fun since I had his expertise, stainless pipe, hydraulic and pneumatic benders, and welders at my disposal... You can buy the flanges online, and 2 45 degree mandrel bends should be all the extra parts your gonna need..

Good luck, have fun, and take pics!

Tommy J

It idles fine when cold but then settles down to under 500 with random roughness. When in park if I press the gas its rough from 500 to 1000 but after that seems smooth and when I let off it is rough from 1000 back to 500. It runs pretty smooth at light acceleration and every so often during acceleration seems to hesitate. At WOT it just does'nt seem to have the power it should, its lacking something plus my exhaust sounds like a tin can as if my back window is open. The muffler heat shield is kind of flimsy and I tied it up higher cause it seemed a little loose. It never backfires. How did you know your cats were plugged? I was wondering if I have an issue with that or bad o2 sensors or something. Its just not running right. Im taking it to Ford tomorrow as a last resort