Tommy J

I know this topic has been beaten to death but Im at my whits end. I have a 2004, 5.4 with 98k. In the last month I've changed the plugs,cop's,(motorcraft), fuel filter, air filter, cleaned the throttle body, maf sensor. New coolant, thermostat and trans fluid and filter. The truck has a pretty steady low idle but lately has a slight roughness to it too(at idle) I tried the relearn procedure after I have been driving it for a while. I don't know if that needs to be done again with the battery disconnected again. I tried my best to look for a vacume leak and even re checked(torqued) the plugs. It idled ok before all of the work but the plugs looked real bad and I think were orig. I just bought the truck so don't know the history. Its not throwing any codes and I know this truck does not have a IAC. It also has a new tensioner and belt because I left a rag under the thermostat housing when changing it and forgot and started the truck to the horrifying sound of tensioner snapping in half and belt shredding. Broke a piece off of one fan blade too. Im paronoid as heck that i did'nt do some unforseen damage with that screw up. i don't see anything obvious. Anyway, is there something i might be missing? I know a new plug or coil could be bad but Im a low tech guy and can't seem to figure out the low idle. It otherwise drives good and does'nt stall or anything. Any insight would be appreciated. Its bad enough i did all of this work in freezing weather and its only 22f today. thanks

Summers22

iTrader: (2)

I would try the relearn again. Cant hurt and it's free. Did you take the throttle body off to clean it?

taylorbowl119

I've got the same problem, and I saw you tried to look for a vacuum leak. But to throw my 2 cents in, I've got a very audible hissing sound under my hood. Mine sounds like it's coming from deeper in the engine, so try to start the truck and just listen really well for a hiss. I'm pretty sure that's my problem and we are having the same issues. I'm going to find the leak soon and I'll try to let you know of thats the problem

Tommy J

Yep, took it off and cleaned the heck out of it. Tried the relearn today without starting from discconnecting the battery if that matters or not and no change

Tommy J

Sometimes I think I can hear something from my drivers side but just can't tell. I poke around and wiggle different lines( I know, not the proper way) but get no change in the idle. Yesterday I replaced the fuel pump driver module near spare tire and no change. It only idles a little rough when my fan speeds up. I agree about a vac leak and dont know where the elbow is that everybody talks about being hard to get at. the only line I see is the red one going behind the engine but dont think its loose. The gas vapor hose looks bad but don't think thats the issue either. Let me know if you find anything

bwFX42006

When my fuel pump driver module went out I had low idle problems as well. Did you check your FPDM under the spare tire? These corrode and cause problems, I was driving down the interstate when mine gave out, the truck lost power, was struggling to get fuel and had a low idle. I replaced it and it worked fine. I would check that, could be causing your problems, especially since it's winter time and it has more exposure to water.

ajack

I'm having the same exact problem as you. It gets worse as it gets warmer and gets WAY worse when it's warm and the A/C compressor is engaged. No codes and nothing is really showing that I have an vac leaks like tripping on acceleration or weird fuel trims. I've been told it's the cam phasers but rarely do I ever read about anyone replacing cam phasers for these symptoms. Occasionally, I get a completely random misfire at load. I'm talking like 1 every 20 minutes of driving and it's on random cylinders. I've done all the same maintenance you have too.

Tommy J

Yep, replaced my badly corroded FPDM with no changes

ajack

Any update Tommy J?

Tommy J

I ordered all 8 refurbished injectors from Rock Auto and should have them tomorrow. Got sidetracked working on my wife's Acura TL, talk about a pain in the neck car to work on. Anyway I figured this would be my last effort to try and solve this idle prob. When I changed the fuel filter it was horrible so Im sure the injectors are'nt in great shape either. It can't do any harm. Don't think I have a vac leak and I guess it could be one of my new plugs or cops but no codes still. The mechanic and a diagnostic is my next step if this does'nt work. Im tired of working on this truck in the dang cold. Its bad enough I saw my power steering lines are starting to leak too. The kicker of all of this is that the last owner of this truck was a Ford mechanic who bought this for his wife and she ultimately did'nt like driving it with young kids. He obviously did'nt have too much time to work on this truck but the floor mats are nice. I"ll let you guys know my results. Take care