Rough Idle After Refuel

[Lvlvl]

Hi all, I drive a 2015 Ford Fiesta Se and within the past few weeks, whenever I fill my tank back up, my idle is particularly rough when I come to a full stop. The speedometer will occasionally dip to around 600-700 before jolting back up to 800-900 while at a stop.

Today I had the worst idle drop to around 500-600 before shooting back up 800-900rpm. This happens regardless of the octane and I do not "top of the tank" as a number of other forums have suggested may be the problem.

My throttle body looks clean, was thinking maybe a fuel filter needs to be changed. What do you all think? Thanks in advance.

 

[scotman]

Hi. The fuel system on our Fiestas cannot be "packed". It will just pittle onto the ground behind the left rear wheel.
There also isn't a conventional fuel filter. Its integral to the pump assembly. If it was restricted, you would have a starvation or lean idle misfire.
Do you have a check engine light when this behavior occurs? And am i correct that it only happens after you have filled the tank?
At what point does the rough idle and rpm spikes stop?

 

[Lvlvl]

No check engine light during the rough idle, already replaced the sparkplugs and used some STP 5-in-1 to clean the injectors. While at higher speeds/rpm there haven't been problems.

The first stop after fuel refill is definitely the worst rough idle period. As the tank empties, the idle seems to get better but still noticeable.

 

[LionsTooth]

Could be evaporative hoses leaking or a bad gas cap? If you have the no-cap model, the inner "cap" should be sealed when closed....maybe it is leaking air? Maybe a fuel vapor purge valve issue?

 

[Lvlvl]

Could be evaporative hoses leaking or a bad gas cap? If you have the no-cap model, the inner "cap" should be sealed when closed....maybe it is leaking air? Maybe a fuel vapor purge valve issue?

Hmm, I do in fact have the no cap model Fiesta. From what I can tell the inner cap is closed as I could not open it without a using a gas can.

I'll have to look into the fuel vapor valve.

 

[scotman]

If you had a faulty seal of the filler tube, you would have an Evap Mil. Same with the canister vapor purge valve. You would have a Mil. The purge valve and the vapor hoses are fairly expensive. The cannister is very expensive. A purge valve failure generally makes itself known to you by making it very difficult to fill the tank.
I would become very interested in the driver module for the fuel pump. First is checking the ground connection to that pump driver module.
Have you noticed any surge condition when driving at a steady speed? It could be that the module is getting a bad signal. I am focusing on this component because it is designed to function across a range of demand signals and is rather numb to intermittent signal noise.

 

[Lvlvl]

If you had a faulty seal of the filler tube, you would have an Evap Mil. Same with the canister vapor purge valve. You would have a Mil. The purge valve and the vapor hoses are fairly expensive. The cannister is very expensive. A purge valve failure generally makes itself known to you by making it very difficult to fill the tank.
I would become very interested in the driver module for the fuel pump. First is checking the ground connection to that pump driver module.
Have you noticed any surge condition when driving at a steady speed? It could be that the module is getting a bad signal. I am focusing on this component because it is designed to function across a range of demand signals and is rather numb to intermittent signal noise.

Now that you mention it, there's been a slight bit of engine surge while on the highway/interstate.

I understand that the fuel pump itself is under the rear seats, is the driver module located there as well?

 

[scotman]

It's under the driver's seat. You might need to pull the seat out to inspect the condition of the harness and connectors. Disconnect the battery before messing with anything under there. You have an airbag in the seatback! You should also locate and inspect the fuse and terminal condition of that FPDM circuit.

 

[Lvlvl]

UPDATE: I have yet to inspect the driver module as I've been swamped between transitioning jobs. After driving for a week and a half looking for more symptoms, I've noticed that as the fuel tank empties, the problems nearly go away entirely. Currently at half a tank of fuel and virtually no rough idle.

 

[scotman]

Good. At least the car is drivable for now. You really should plan to have a ford service technician throw some of his skill and equipment at that issue ASAP.
If something is failing, the condition will evolve and change to the point that you will become stranded at some point. You should keep in mind that an hour and a half of dealership service department diagnosis labor time is still cheaper than a 40 mile tow fee!
Please keep us posted on the outcome of this strange issue.

 

[Handy Andy]

This may help...

Turn key to "On" position (where you see all your ICON lights..).

Keep key at ON don't "start"

As those lights wink out, locate the "Engine" icon...

Wait about ten seconds - the "Engine" Icon will remain on.

But...if there is a problem where it can't pass Emission testing - the Engine Icon light will blink for a 7~8 second duration - AFTER it's self-diagnostic routine - then stay on.

Then grab yourself a OBD-II scanner and verify that the MIL is NOT on, but one of the 7~9 I/M monitors will show NOT READY as you scroll thru the scanner tools I/M Monitor list - it won't store any codes until this condition (Emission) will not clear on several tankful's - so you may need to drive full to empty on several trips to determine this fault and if it won't clear.