Jeremy Tripp

Alright guys, I see tons of posts about the low idle and dying at stops, but none quite match my symptoms. Hoping you can help. Please note, I am not a mechanic nor do I have access to OBD2 tools or PCM analyzers, so bear with me.

THE GOOD
I'll fire it up, it idles initially at around 1250 then quickly starts to drop to around 700 which I believe is totally normal. When I start driving and come to a complete stop, the idle sits at 550-600 when things are good and the A/C is running. This is usually my sign that I'm gonna make it to where ever I'm going.

THE BAD
Been happening for about a month, very intermittent and it started when the weather changed from cold to hot, although I don't know if that's actually meaningful -- it's usually towards the end of my short 15 minute commute, the idle will start to gradually dip when coming to each stop. First it'll drop to 500, the next stop it'll fall below 500, the next stop below 400. I've seen it dip as low as 250-300 before finally stalling. When accelerating from these low idle states, it will surge a bit as the engine seems to try to catch back up. When it stalls, I'll quickly throw it in Park, turn the key off, then fire it right back up. As of yet, it hasn't stranded me on the side of the road, but I fear it's only a matter of time. When it stalls, I get the battery light and the check engine light. The screen says "Check Gauges". Upon promptly checking the gauges, they tell me absolutely nothing useful (see attachment). Overall when it happens, it seems like whatever is controlling the idle is just slowly "giving up", but it doesn't make sense to me why starting the truck back up temporarily "resets" it long enough to get where I'm going.

THE UGLY
Took it to the shop the first time it happened. They said it had thrown some airflow codes, so they charged me $550 to clean the air intake system: throttle body, fuel injector cleaner, etc. Yes, I now know I could've done this myself for about $20, but a month ago I was young and stupid and needed the truck running again ASAP. So I go pick it up, drive it home, no issues. Next morning commute, it dies again as I'm pulling into the parking lot at work. I take it back, they keep it for 2 days, find nothing, they tell me "it might need to get worse before we can fix it." I pick it up, drive it home, no issues. A few days pass and it's not dying, but instead I'm getting a lot of unusual "surging" or "bucking" behavior. Eventually it starts in with the low idle and stalling. Again, very intermittently, but probably every other or every third time I drive it. So I take it back with all the anecdotal data I collected, none of which really identifies any trends in terms of how to reproduce it. They keep it another 2 days, find nothing, fix nothing, they tell me since they can't reproduce it and it's no longer throwing any codes from when it's happening to me, there's nothing they can do except start replacing things and hope for the best. They tell me my best option is to take it to a Ford Dealership and have them reset the idle to something higher -- this truck is not worth the $1000 a Ford Dealership will charge me just to pull it into their shop, so this is not an option (it also sounds like a band-aid, not a fix). They also say I could try replacing the throttle body assembly as a first step.

MY RESEARCH
The day I got it back after the last shop visit, I went ahead and put it through the relearning procedure. My suspicion is that the shop didn't do this after cleaning the throttle body the first time, which likely caused the bizarre surging behavior since I haven't experienced that same behavior since then. The relearning procedure seemed to buy me 3 straight days of no issues until yesterday -- it was either that or the fresh tank of gas -- OR it's all random and I'm still clueless. From what I've read, there could be a number of things at play here: MAF, Throttle Body, TPS, PCV hose, IAC (although I think I've gathered the 5.4Ls don't have the dedicated IAC -- is this accurate?). When reading the symptoms of other folks who've had any one of these components fail, they cite similar, but still different symptoms -- namely surging at highway speeds. By contrast, the highway is the only time I feel "safe" driving right now -- no issues there. And again, folks with those issues don't seem to report the gradually decreasing idle RPMs until ultimate stall. They typically just report a generally low idle and stall at stops. I don't know if they're just leaving out the details or if this is truly a different symptom.

NEXT STEP
I'm trying to work my way up the least expensive options here. This baby has 183k miles on it. It's had a good life. I'd like to resolve this issue so I can sell it next month after I close on a house, so I'm not looking to put a bunch of money into it. I'm thinking my next best move is to go ahead and replace the throttle body assembly. I believe these include the TPS so it's two birds with one $130 stone. Before I place the order, I'm just looking for some guidance on whether that has an actual chance to fix this or am I barking up the wrong tree? Thanks for getting this far. Anyone who's been in this situation knows how maddening it can be and I truly appreciate any help.

Any questions or other info I can provide? Please let me know. Again, I don't have the tools to analyze computer data, but the shop who had it for a total of 6 days tells me it wasn't reading anything out of the ordinary.

Just stalled.

redfishtd

Pcm sends coded signal to board on side of motor on throttle body . TPS sends throttle plate position back to PCM . If board screws up or motor or sticking mechanical problem then throttle body will have to be replaced . New OEM comes with TPS on it . Mine failed when throttling up intermittently over weeks PCM would go into failsafe and it would shutdown .
A new throttle body is what most would advise at this point . Cheapest way to go since labor is so high . Mine was $200 on ebay select and was new model .2005 had a bad series from factory .

Jeremy Tripp

Right on. It sounds like TB is the next best/cheapest move. Thanks for the sanity check and the reply.