Accelerates after gear change

[jimmytheford]

Hi,

My daughter has a 2017 Ford Fiesta 1.2 petrol-engine car that has a very occasional problem. When she changes gear in traffic, so going slow, as she re-engages the clutch the car starts to accelerate rapidly when she hasn’t pushed the accelerator pedal down. It has decelerated when she disengages the clutch but often she turns the engine off to stop it. Sorry the details are a bit sketchy because it happens very infrequently and, when it does, she is trying to slow/stop the car rather than note exactly what occurred and fault find.

I’ve driven the car myself and accompanied her but, because it is very occasional, it hasn’t occurred with me in the car. Apart from this the car seems normal, idle is stable and accelerates OK (it has only done 20,000 miles). She tells me it is sometimes difficult to get into first gear, but I haven’t experienced this (maybe because of my old driving style developed on cars with poor gear boxes).

I’ve found a thread that had a problem with unstable idling and un-commanded acceleration but it doesn’t fit her symptoms of the gear change.

I’m more familiar with cars with a mechanical link to a carburettor. I’m not sure but I think her accelerator pedal has a potentiometer for sensing its position that connects to the throttle control unit, is that correct?

Does anyone have any experience of this problem? I wondered if there may be a Ford service bulletin covering this but I haven’t found a shop manual or service bulletins on line yet.

Would appreciate any help and thoughts on what may be wrong.

[alexp999]

Is it possible she's changing up too early on occasion?

Modern cars have anti-stall and also a creep/crawl aid.

Basically you can move at low speed with just the clutch and the car will put in a minimum amount of throttle to support it. I'm imagining if you change gear too early you could get the same which may feel a bit like a surge of acceleration if you're not expecting it.

[DaveT70]

Tell her when it happens, not to panic, but to just repress the clutch back down until the revs settle.

The emissions control will make the engine rev if the sensor senses unburnt fuel so check the coil pack, leads and plugs are in good condition first, that the air cleaner is clean and not damp and clean the MAF sensor.

If that doesn't solve the problem then the throttle body is probably very dirty and is sticking, take it off and clean it

[jimmytheford]

Hi Alex and Dave,

Thank you very much for your help and advice.

I did try moving it into second and third gears at low road speed and it didn't mis behave for me; but my gear change may be different to my daughters.

She has had it serviced recently; in between events so it wasn't something done then. The air filter was replaced so that should be good ( but I'll check it when she visits next).

I haven't got a workshop manual but Is the MAF sensor on the air filter box, near the large outlet duct that I guess goes to the Throttle body on the engine?

Kind regards

Jim

 

[DaveT70]

1 hour ago, jimmytheford said:

I haven't got a workshop manual but Is the MAF sensor on the air filter box, near the large outlet duct that I guess goes to the Throttle body on the engine?

Yes

[jimmytheford]

Hi Alex and Dave,

I found a couple of videos on the internet showing the MAF filter and throttle body; hopefully my daughter's car will be similar.

kind regards

Jim

[gds1972]

As a just incase if you have floor mats fitted to the car try taking them out to see if that changes anything.

[DaveT70]

On 1/13/2023 at 1:19 PM, gds1972 said:

As a just incase if you have floor mats fitted to the car try taking them out to see if that changes anything.

Yes, good point

[Eric Bloodaxe]

On 1/12/2023 at 12:33 PM, jimmytheford said:

I did try moving it into second and third gears at low road speed and it didn't mis behave for me; but my gear change may be different to my daughters.

If it doesn't do it for you it does suggest driving technique and support Alex's explanation above.

When driving in slow traffic, I often just let up the clutch in first to set off without touching the accelerator. Experimentally, I have tried changing up through second and third, again without touching the accelerator and the car more or less drives itself.

Similarly to Gordon's point above, even small changes in seat position can affect your driving by preventing you getting on/off the clutch properly, particularly if you have a 3 door and often fold the drivers seat to put people or stuff in the back.

My Mrs is notorious for this and I often get in her (3 door) car and find the seat in a weird position!

 

[jimmytheford]

Hi All,

Thanks for all the help, thoughts and advice.

I went over to see my daughter's car yesterday; the air filter was new. I looked at the throttle valve and it was very clean inside apart from a small amount of "gunk" around the edge of the plate and the body where the plate rests. I cleaned it off and put it back together. The leads looked in good condition. The car  worked OK for me on a short run around the block. I don't think this proves anything though because she can drive for 20 minutes and not have a problem herself; it only happens very occasionally.  For example it didn't happen today on the way to work or back with her driving.

I didn't have much time to do anything else before it went dark; I had a small leak on her washing machine outlet to fix while I was there. I was going to clean the MAF sensor but it wasn't where I thought it would be (in the tube between the air filter and throttle valve) having looked at some videos on-line.

I'm hoping the gunk in the valve was the cause but it didn't seem much to me. If it reoccurs I'll suggests she takes the mat out and try to find the MAF sensor.

Thanks again,

Jim

 

[Marky146]

Daft question but does the car have cruise control fitted?

[jimmytheford]

Hi Mark,

I don't drive her car very often, only when there is a problem so I don't know but I'll ask her to check (I've sent her a picture of the  cruise control buttons).

Are you thinking she may be pressing the resume button accidentally?

Kind regards

Jim

 

 

[Eric Bloodaxe]

The actual trim of the car has not been mentioned, but as far as I can remember the 1.25 was only available up to Zetec trim (which didn't have cruise). I think cruise was available on the Titanium but by then the base engine on the Titanium was the 80ps non-turbo triple.

[jimmytheford]

Hi,

Sorry for the delay in replying; few things got in the way - COVID for one.

She sent me a picture of the steering wheel and it doesn't have cruse control as Roger stated above. 

She has tried to adapt her driving and seems to be coping with these "features" ( un-commanded acceleration after gear change and stiff gear change) although the way she described it to me it doesn't seem right.

If I get any further update to report on this I'll post it.

Thanks for all your help/thoughts,

Jim

 

 

[jimmytheford]

Hi,

I thought this problem had gone away but my daughter visited this week and as she drove home the problem reoccurred. She drove back, with great difficulty, and I got in the car. I put my foot clutch for a while before selecting first but couldn't change into gear. Turned the ignition on and off, put the clutch in and put it into first gear with my foot on the clutch. After a few seconds the clutch started to re-engage with my foot on the pedal. I repeated this several times. My daughter confirmed this is similar to what has been happening in the past. 

I think there must be a leak on the clutch hydraulics, the master cylinder,  "slave" cylinder or pipe between them. There doesn't seem to much fluid lost from the brake reservoir (which I think is shared with the clutch system) so I guess it is the clutch master cylinder rather than the pipe or slave cylinder. On some cars I think the master cylinder seal can leak and allow the fluid back into the reservoir. There is no evidence of fluid below the clutch pedal, clutch housing or around the bleed nipple.

Would appreciate anyone's thoughts. on whether the master cylinder is the most likely cause.

Kind regards

Jim

[RL123]

If the clutch is slowly re-ingaging whist still having the pedal depressed, it would suggest a poor seal in the Hydraulic system. As you say you are not loosing fluid, it could suggest the Master cylinder seal which prevents fluid returning to the reservoir is letting fluid by.

I cannot see how it would relate to the title of the post though. It could make the bite point of the clutch variable and obviously clutch drag would make gear selection tricky.

 

[RL123]

An added thought. If the pressure in the clutch hydraulic pipe reduces due to leak back this could trigger the throttle uplift from idle especially if left in gear.

[jimmytheford]

Hi Roger,

Thanks for your reply. I think you must be right that the seal on the fluid intake must have failed. I've tried to find a break down/diagram of the fiesta clutch master cylinder internals but can't find one.

The title was based on what my daughter told me was the problem at the time; I could never get the problem to occur when I drove it until this week. I think she meant the car started to accelerate/move sometimes after she changed gear; but forgot to say she still had her foot on the clutch pedal. 

Kind regards

Jim

 

 

[RL123]

Hi Jim,

     The master cylinder usually has a seal on the inner end of the piston, probably spring loaded that closes the feed from the reservoir when pressed. A long while since I’ve stripped one down.

Are they still serviceable or maybe replacement cylinder

Roger

 

[jimmytheford]

Hi Roger,

Thanks for the reply. I thought there must be a stop valve to prevent the fluid flowing back to the reservoir when the pedal is pressed/piston moves.

I could find a repair kit only replacement cylinders on-line.

Kind regards

Jim

 

[RL123]

Hi Jim, Thanks for the update, my 2021 Kuga 8k miles, goes in next week for a new clutch master cylinder. Leaking on my foot.

kind regards 

Roger

[jimmytheford]

Hi All,

Just a quick update. My daughter's car had the clutch master cylinder changed and it seems (touch wood!) to have solved the problem for now. At least she can put the clutch pedal down and it remains disengaged. 

Hope your Kuga is ok as well Roger.

Thanks to everyone for their helpful advice.

Jim

 

 

[RL123]

Thanks for the update, my Kuga had a new clutch master cylinder under warranty and it also required a complete new pedal as it cannot be serviced separately. Thankfully not at my cost.

[jimmytheford]

Hope the new clutch master cylinder fixed your problem Roger.

I asked for the removed Master Cylinder so I could check it out with fluid. I did that and it seemed to function correctly with no leak back to the reservoir input under pressure.

My daughter said she thought it misbehaved again today although she couldn't be sure. She was at a junction concentrating on the traffic so couldn't recall what exactly happened. She checked the brake/clutch reservoir level when she got home and it was still on Max so no significant fluid loss.

I was wondering if air could be entering the hydraulic system and cause the clutch to re-engage with the pedal pressed? I will drive it when I see her next and check if pressing the pedal down for a long while results in the clutch re-engaging. Apart from this I'm not sure how to fault-find this so would appreciate any help/thoughts again.

Kind regards

Jim

[RL123]

My father had an issue with his Classic Capri. Highly unlikely to be yours.

He had just had the clutch replaced and was needing to manually adjust the push rod to disengage the clutch. It turned out to be the Main Dealer had not tightened the bell housing bolts and the gearbox was moving away from the engine.

As I said highly unlikely in your case.