Hello,
Noob here. I have a 1999 E250 5.4L Triton. Question, just recently my van started doing this.
While idling, when I input throttle to drive or even in park for that matter. My van will for a brief moment drop RPMs, as if it it might stall, and then then power comes on and it is fine. If I slowly, slowly add throttle input, then it seems to be fine.
I recently added a new MAF sensor before this occurred after a 0171 code. The new MAF sensor made a nice improvement in performance I might add. No check engine light since.
Since these new symptom of dropping off, I cleaned the throttle body with cleaner spray. No change. Still present.
Other than that it seems to drive fine and has power when I apply power when driving down the road.
No check engine light at the moment.
Thank you, I hope my vague question reveals some guidance.
Appreciate y'all!
Photo of my van. @Azimuth_Everywhere on Instagram. It is a work in progress.

 

What is the 8th character of your VIN. L or M or Z?
You can have a hundred of DTCs (diagnostic trouble code) without triggering a CEL (check engine light). So can you do a scan on that?
Have you checked and changed your air filter?

 

If you can,,,,
Autozone will scan your vehicle for any codes with no charge. Post the codes here, and we will try to offer some suggestions that might help. The codes should provide some directions as to where to start checking. I don't know if they can/will provide a written copy, doesn't hurt to ask.

There are some possibles, but it would be like shooting in the dark, so best to wait and see how you make out, thanks.

 

The 8th letter is "L"

 

Below is the Locations index page of All-Locations.pdf

Below is the Diagrams index page of All-Diagrams.pdf



When you don't have the exact DTC without a CEL, it also indicates that the issue is not critical enough, so I can only try to cover as much relevant info as possible.
The All-xxx.pdf attached below, they are huge pdf and complete, I have created just the index page snapshots so you can navigate and follow easier. The All-Pinpoint_Test.pdf covers all the tests and I randomly picked out a few for you.
All I can suggest, before throwing parts at it, any sensor you remove, clean accordingly. Electrical connector, clean both ends using contact cleaner or 91% isopropyl alcohol.

 

Looking back at the original problem of the 171 code, a MAF sensor or IAC unit will not cause that particular code. There is a problem in the bank 1 air intake (pass side bank)
Problems from MAF and IAC will affect both banks.
What might be happening, the mixture for those cyls is lean (unmeasured air)and they are receiving insufficient fuel, reported by the oxygen sensor for that bank.
When you depress the throttle pedal, now the MAF reports the incoming air and the computer corrects the injector on time and the engine smooths out.
Look for a possible vacuum leak with something that might be connected to the intake for that bank or intake leak on that side where manifold is bolted to engine.

 

thank you

 

I’m having the same problem with a rough idle after it warms up but runs well once rpm is above 10K on an E250 5.4L.
Replaced the PCV valve yesterday (auto zone code) with the issues reoccurring.
Im going to take it to a shop but locally they are notorious for just throwing parts at it so I’d love have some more ideas of what the root causes may be.
It’s got 180K on it so I don’t mind replacing some parts that should be at/close to the end of their serviceable life - just as long as it’ll fix the problem at hand and potentially stop additional downstream issues from coming up. This is my service van so it’s not like I can just leave it in the shop for extended periods of time while I roll a rental for a bit. I’d really like to get it done te first time- maybe wishful thinking 🤷‍♂️

Dd you find the issue?