Technical Jerking when letting off the accelerator

[Tessia]

Fiat 500 2008 1.2

I started having a horrible jerking back and forth when I take my foot off the accelerator, at first I put it down to myself being a new driver with poor clutch control but I'm starting to suspect it's the car.

When I put my foot back on the accelerator, the jerking stops. If I press in the clutch before taking my foot off the accelerator I don't get the jerking and if I ease of the accelerator slowly, I also don't get the issue however I do have to come off very, very slowly, more so then what feel normal, I've driven a few other cars and never had this issue. Putting my foot on the accelerator doesn't cause any issues, only releasing it.

After a bit of googling and a suggestion in another post I made I came across two potential problems, the rear engine mount and air in the clutch lines. Reading about air in the clutch lines I don't think it is that but I will bleed them in the next couple of days to be sure.

Can anyone tell by looking at the pictures below if this mount looks OK? If it looks OK, does anyone have any other ideas?

Edit: if it's not possible to tell from pictures alone, how can I test it to be sure?

It only really happens in 1st and 2nd gear, it happens in 3rd sometimes but nowhere near as aggressive.

 

[bugsymike]

Looking at your "dog bone" engine stabiliser in the photo it doesn't look bad , however it may be an idea to see if it moves a lot when leverage is applied, in case it is soft rubber/cheap pattern part.
I would have gone for that mounting first as a common issue on many makes of front wheel drive vehicles, though it may be an idea to check to top mounts also.
It's difficult without driving a car to diagnose correctly as many things can cause similar problems.
Generally it shouldn't carry on jerking once foot is off or on pedal as the change in load should only move the engine once in that direction, forward or back, so if longer jerking issue may be something else.
Unlikely to be clutch side as in hydraulics, if it does it only by moving the accelerator.
However if car has a "DMF" dual mass flywheel they can cause a snatch in transmission if badly worn, but I would have thought some metallic noise around that area with bonnet up may be noticed.

 

[Tessia]

Looking at your "dog bone" engine stabiliser in the photo it doesn't look bad , however it may be an idea to see if it moves a lot when leverage is applied, in case it is soft rubber/cheap pattern part.
I would have gone for that mounting first as a common issue on many makes of front wheel drive vehicles, though it may be an idea to check to top mounts also.
It's difficult without driving a car to diagnose correctly as many things can cause similar problems.
Generally it shouldn't carry on jerking once foot is off or on pedal as the change in load should only move the engine once in that direction, forward or back, so if longer jerking issue may be something else.
Unlikely to be clutch side as in hydraulics, if it does it only by moving the accelerator.
However if car has a "DMF" dual mass flywheel they can cause a snatch in transmission if badly worn, but I would have thought some metallic noise around that area with bonnet up may be noticed.

Thank you for the reply.
I'll jack the car up, drop it on some stands (maybe just drive it up the ramps if there's enough clearance), put the jack under the mount and see if it moves. I'll also take a look at the other two mounts and see how they look.
Once my foot is off the accelerator it does continue to jerk for a second or two and is quite aggressive.
The only noise I have noticed with the bonnet open is when the radiator fan turns on, possibly a bad bearing but that's another issue.
Once my dad is back off holiday I'll ask him to do a test drive as he has a much better feel for this kind of thing.
I have a trip to wales planned in a few weeks and really want it sorted before then.

Edit: I forgot to mention, it only really happens in 1st and 2nd gear, it happens in 3rd sometimes but nowhere near as aggressive.

 

[bugsymike]

Thank you for the reply.
I'll jack the car up, drop it on some stands (maybe just drive it up the ramps if there's enough clearance), put the jack under the mount and see if it moves. I'll also take a look at the other two mounts and see how they look.
Once my foot is off the accelerator it does continue to jerk for a second or two and is quite aggressive.
The only noise I have noticed with the bonnet open is when the radiator fan turns on, possibly a bad bearing but that's another issue.
Once my dad is back off holiday I'll ask him to do a test drive as he has a much better feel for this kind of thing.
I have a trip to wales planned in a few weeks and really want it sorted before then.

Edit: I forgot to mention, it only really happens in 1st and 2nd gear, it happens in 3rd sometimes but nowhere near as aggressive.

The jack under the mount will be less effective as a test , the movement is forward and backward , basically the engine hangs from the two top mounts but the one on the bottom stops it from moving front to rear, so as long as the car is safely supported try and move the sump area forward and back.
For the jerking to continue with foot off the pedal doesn't really match with a engine mount issue to me.
The torque effect in lower gears makes it more noticeable.
Good to have dad as a second opinion, it's what makes us feel useful.

 

[Tessia]

The jack under the mount will be less effective as a test , the movement is forward and backward , basically the engine hangs from the two top mounts but the one on the bottom stops it from moving front to rear, so as long as the car is safely supported try and move the sump area forward and back.
For the jerking to continue with foot off the pedal doesn't really match with a engine mount issue to me.
The torque effect in lower gears makes it more noticeable.
Good to have dad as a second opinion, it's what makes us feel useful.

Ah yeah, makes sence, ill give that a go.
I told him about the issue and he's more then happy to "test" it for me tomorrow. He's an ex rally driver and finds this car very fun to drive, I may not get it back

 

[Tessia]

The jack under the mount will be less effective as a test , the movement is forward and backward , basically the engine hangs from the two top mounts but the one on the bottom stops it from moving front to rear, so as long as the car is safely supported try and move the sump area forward and back.
For the jerking to continue with foot off the pedal doesn't really match with a engine mount issue to me.
The torque effect in lower gears makes it more noticeable.
Good to have dad as a second opinion, it's what makes us feel useful.

I tried pushing on the engine and there is a fair amount of play as seen in the video below. Is that normal or excessive?

 

[bugsymike]

I tried pushing on the engine and there is a fair amount of play as seen in the video below. Is that normal or excessive?

Does seem quite a lot, more than the look of the mounting indicated. Is there any signs of the rubber separating from the metal of the bush?
There are probably some good suppliers other Forum members can recommend , but recently I fitted some after market Black Powerflex suspension bushes on a Skoda Scout 4X4 and was really impressed how much it tightened it up.

 

[Tessia]

Does seem quite a lot, more than the look of the mounting indicated. Is there any signs of the rubber separating from the metal of the bush?
There are probably some good suppliers other Forum members can recommend , but recently I fitted some after market Black Powerflex suspension bushes on a Skoda Scout 4X4 and was really impressed how much it tightened it up.

Not that I can see. There does seem to be a bit of loose rubber flapping around in this photo though.
The car was only bought last week so I'll take it back to them and try and get them to sort it out, I'd just like to narrow it down as best as possible before I get in contact with them.

Edit: I had a look at those powerflex things, might be a good idea to add one if I end up getting a new mount fitted.

 

[bugsymike]

Does look a bit suspicious, can you see any more movement or breaking away of the rubber when you put a bar or lever to move it?

 

[Tessia]

Does look a bit suspicious, can you see any more movement or breaking away of the rubber when you put a bar or lever to move it?

I haven't had chance to look yet.

I have noticed that the jerking can also happen when accelerating in 1st or 2nd if I've had the clutch in and then let it out and accelerate but it depends on the revs and speed. Accelerating from a stop doesn't cause it.

My dad got back early and came to have a look. He watched the engine as I revved it and said it is moving more then he would expect it to.

To play it safe we're going to take it to a garage and get them to check it over, hopefully whatever it is is covered under warranty.

Thanks for all your help and advice. Even if I don't end up fixing it myself, I've still learned a fair bit from this.

 

[varesecrazy]

Hopefully the g.box end bolt will clear the exhaust.. had a similar hassle with the dogbone on my diesel

It was so worn it banged as you changed gear... only @£20 for a new one

 

[Tessia]

Hopefully the g.box end bolt will clear the exhaust.. had a similar hassle with the dogbone on my diesel

It was so worn it banged as you changed gear... only @£20 for a new one

I'll take any repair that's only double digits!

 

[John202020]

Is it most apparent in 2nd/3rd gear by any chance? especially when cold?

 

[Tessia]

Is it most apparent in 2nd/3rd gear by any chance? especially when cold?

I'd say 1st and 2nd are the worst and I think it's just as bad whether it's hot or cold.

 

[John202020]

Our 09 1.2 does this at times, I think its when the ecu gets confused typically at only slight throttle, to stop it dip the clutch immediately it starts or it will get really jerky simplest way is to change up a gear never investigated why as its not all the time, though we have a odd accelerator pedal response in that you can't hold the car at say 2k Revs whilst stationary

 

[Ralf S.]

I'd change that mount.

The movement looks excessive and the rubber is breaking up, so odds on that it's the cause of the shunting. The engine mounts might also be contributing to it.. but bushes tend to work until they don't, so if there's no visible signs of deterioration on the engine mounts, then they're likely to be okay.. Anyhow, a new bottom mount will highlight any other excessive movement, so do that one first.


Ralf S.

 

[Tessia]

Our 09 1.2 does this at times, I think its when the ecu gets confused typically at only slight throttle, to stop it dip the clutch immediately it starts or it will get really jerky simplest way is to change up a gear never investigated why as its not all the time, though we have a odd accelerator pedal response in that you can't hold the car at say 2k Revs whilst stationary

Yeah I've quickly learnt to use the clutch to stop it. I don't suppose you've had your rear mount checked? I could be talking nonsense but could the temperature be effecting the rubber which could explain why it only happens sometimes?

 

[Tessia]

I'd change that mount.

The movement looks excessive and the rubber is breaking up, so odds on that it's the cause of the shunting. The engine mounts might also be contributing to it.. but bushes tend to work until they don't, so if there's no visible signs of deterioration on the engine mounts, then they're likely to be okay.. Anyhow, a new bottom mount will highlight any other excessive movement, so do that one first.


Ralf S.

I'm definitely going to take it in to a garage to get that mount looked at. I would happily do it myself but I've only had the car a week so if that's the issue it's the dealers responsibility.
I'll ask them to check on the top two mounts too to be safe.
Thank you.

 

[John202020]

Yeah I've quickly learnt to use the clutch to stop it. I don't suppose you've had your rear mount checked? I could be talking nonsense but could the temperature be effecting the rubber which could explain why it only happens sometimes?

Not looked at the mount but will when I do the oil change 100k and 14 years old

 

[Tessia]

Not looked at the mount but will when I do the oil change 100k and 14 years old

97k and 15 years here. What colour is yours? I didn't have a choice but ended up with yellow and love it!!