Puretech 1.2 130 Automatic - hiccups when acceleration with heavy load

[RMSSA]

Hi everyone,

my car is showing since a while an unstable / stuttering acceleration on very specific conditions...
It only happens with
- full car, heavy loaded (full trunk)
- after a couple of hours driving
- going uphill and trying to increase speed, to overtake for example.

if I press the gas pedal to try to accelerate, the car stutters a few times while slowly increasing speed

if I accelerate on a flat or if the car is not loaded, everything is fine. If I increase the speed slowly, also fine. I can stay at higher speeds with no issues, it's the acceleration that is the problem. It doesn't seem to happen on first 2-3hrs of travelling

Basically only happens when I make long family trips on vacation with a full car...

I've had problems with the lovely wet belt around 66k kms, where it was replaced and oil circuit cleaned up. I've been visually checking the belt since then and seems to be OK.
Car is now around 99k and plugs were replaced about 12k ago. I've only noticed this behavior after the plugs were replaced, but given it#s so sporadic, I can't garatee was not happening already before.

After some online search I think it can be spark plugs, coils or something in the fuel injection system. However since this is so sporadic and in hard to replicate conditions, I am unable to do a test drive with a mechanic and show it happening and I just came back from the mechanic place and they could not find any error messages via OBD...

So I'm kind of stuck to wait for it to get worse or start guessing...

Any ideas or similar experiences?

Thanks

[Multispacer]

Hi everyone,

my car is showing since a while an unstable / stuttering acceleration on very specific conditions...
It only happens with
- full car, heavy loaded (full trunk)
- after a couple of hours driving
- going uphill and trying to increase speed, to overtake for example.

if I press the gas pedal to try to accelerate, the car stutters a few times while slowly increasing speed

if I accelerate on a flat or if the car is not loaded, everything is fine. If I increase the speed slowly, also fine. I can stay at higher speeds with no issues, it's the acceleration that is the problem. It doesn't seem to happen on first 2-3hrs of travelling

Basically only happens when I make long family trips on vacation with a full car...

I've had problems with the lovely wet belt around 66k kms, where it was replaced and oil circuit cleaned up. I've been visually checking the belt since then and seems to be OK.
Car is now around 99k and plugs were replaced about 12k ago. I've only noticed this behavior after the plugs were replaced, but given it#s so sporadic, I can't garatee was not happening already before.

After some online search I think it can be spark plugs, coils or something in the fuel injection system. However since this is so sporadic and in hard to replicate conditions, I am unable to do a test drive with a mechanic and show it happening and I just came back from the mechanic place and they could not find any error messages via OBD...

So I'm kind of stuck to wait for it to get worse or start guessing...

Any ideas or similar experiences?

Thanks

The first thing to replace I would think is the spark plugs again [with a different make] as it has been known for faulty batches of plugs to get into the market.  

If the prblem still persists, I would start to look at the auto box as it sounds as if the problem is occuring when under load or after travelling for a while then maybe an intermittent fault in the auto gearbox, or maybe even something like the gearbox oil needs replacing/topping up?

[RMSSA]

Yes, I think I will ask them to replace the spark plugs again next service which is due soon. It's so hard to reproduce that I don't want to start on a trial and error troubleshooting that will get very expensive, very fast

Apart from the auto transmission, any other ideas? Injector? fuel pump /filter?