Alright, this is driving me nuts, truck (not mine, family, so I’m committed) 2003 5.4 230,000 hard soccer Mum miles. Cold days would get the P0171and P0174, but I’d clear the code and would be fine. Started running rough a week or two ago with the CEL flashing, code was that multiple cylinder misfire cant remember the code. So I replaced the plugs, which were nasty, corroded, and some of the boots fell apart. I didn’t know you could buy just the boots so I got two new from O’Rilies. Ran worse after and after a while got the P0171 and P0174. Found this forum, which is great by the way, figured I’d try the smoke machine method. Quickly McGyver’d one up using a lit cigar for the smoke source. Nothing…except for the IAC valve….not knowing any better that has an air bleed on it, I replaced it. Ran the same but would stall in drive, most of the time, and still idle rough and around 1500 rpm’s was the sweet spot for absolutely no power at all.. Checked all the vacuum lines, all the PCV lines, changes the PCV valve, even did the propane wand check with no results. Did the smoke check again, thought I saw the EGR valve leaking slightly, so replaced that, and found one of those EGF sensor lines cracked, replaced, cleaned bunch of crud from the TB, seafoam’d the engine…now it runs the same but doesn’t stall any more. Oh every time I work on this I disconnect the Batt the whole time so I assume the comp resets, so I give it some time to warm up and get adjusted.. I’ve disconnected and plugged most of the VAC lines, replacing the ones that looked bad. So the only common thing I haven’t done is actually remove all the PCV lines and that elbow below the IACV, get plenty of suction on the PCV and cant feel anything leaking at the elbow but am going to pull all tonight.
I am at a loss…could this be an intake manifold leak from somewhere that wont show up on the smoke test? Should I pull all the plugs again and replace the boots, maybe throw the OEM coils back on with new boots. None of them really felt like they made any sort of positive contact, just sitting on the spring a bit. Fuel filter? Was running ok before…
Sorry this is such a long post…
