My recently acquired '99 F350 5.4L 4x2 with 214k.mi. will start normally, and go to a fast idle warmup. Tach shows about 1300rpm. After 90seconds or so, the revs drop a bit... then again at 3:30mins... and there will be ups and downs over the next few minutes til at about 9:20 in the linked video, the idle drops VERY low, the engine 'lopes' a few times as if running on 2 cylinders and then stalls out completely. If you'd care to give it a listen for almost 10mins of video, follow the link. If you just want to hear the moment it does the huge drop and stall, jump to about 9:15 in the video.


Temperature doesn't seem to matter, but on this occasion, the truck has sat unused for 48hrs. The night before the temp dropped to 12 degrees, and it's 11:45am and 18 degrees when the video begins.

It's got a new fuel filter and has run through two tanks of fresh fuel since purchase a month ago. The recent tankful was treated to a dose of dry gas and injector cleaner to try and remedy the issue, but no change whatsoever has occurred.

I figure before I start buying pricey bits or send it to a mechanic for a big-buck fix, maybe somebody can point out the best route to diagnose the issue... or even better, has a quick fix ready to go.

Any thoughts?

 

I did listen/watch to the video...off hand. I would suggest cleaning the Throttle Body Housing (TBH) to start. this attaches to the upper intake.

To clean it, you need to remove it, (it's not that bad of a job really). With the TBH off there should be a couple of interior EGR ports or passages that are probably getting clogged with carbon deposits, but clean the whole TBH and throttle plate. Make sure the EGR ports are cleaned out. While the TBH is off, there should be a smaller cylindrical item on the rear of the TBH that would be very close to the fire wall a vacuum line and a electrical plug on it. That is the Idle Air Control (IAC)...It also can be removed & cleaned.

For the TBH cleaning can be done with carb cleaner. For the IAC, I would use WD40. There is a small rod inside the IAC that needs to move freely. the carb cleanner is a bit too aggresive for the IAC and the WD40 has some lubricating value also. Just make it is dry before reinstalling the IAC to the TBH.

If that doesn't cure it then you probably have some lazy sensors that are not responding well...then you might be wise to take it and have the engine monitored with something that is capable of monitoring the individual sensors, ( Mode 6). MAkeing sure that they are turning on and off in the right time and temperature frames.

might not hurt to have the fuel pressure tested too.

Also....From the video it sounds like you have a heat shield rattling...kinda tinny sound

 

I'm wondering if the Idle Air Controller isn't at fault? Any MIL codes being thrown?

Does it also stall when warm (operating temp) when driving, like at a stop light?

 

Thanks guys, I'll keep these replies handy for when I get started on the issue... if it returns. Today I had it out for 90minutes, and the issue didn't come up. Yes, it did normally stall at a stoplight/sign after 10 seconds or so, but not today. It idled at 760rpm with the slightest hint of a miss, but never did the drop/stall. Maybe that injector cleaner actually, finally got whatever was causing it to come lose and burn off. I'll keep you posted.

Oh, and yes, the shield is loud and very loose. Just hasn't been a priority as the truck hasn't been running daily. Now that it'll be entering daily driver status, I'll have to get after that noise.