Help requested Ford Focus mk3 2013 – car jerks/stutters when

Hello all,

I am reaching out in hopes of finding a solution to a problem that has plagued me and my car for several months now. If this post does not belong here or if any other subreddits may yield better/more useful responses, please let me know.

I have scoured the internet to find the solution to this problem to no avail. The mechanic that my family has used for as long as I can remember has been unable to diagnose and fix the problems I’ve been having. I am hoping that you guys may have the solution...

My car
Ford Focus MK3 (2013)
1.0 ecoboost (gasoline)
Not sure if this is relevant, but the car is originally from Germany

Problem
The problem initially presented as a slightly rough idling of the engine. This slowly developed to misfiring cylinders and jerking when accelerating. Initially, the car only jerked when accelerating full throttle. As the issue progressed, the problem started to occur at half throttle as well. At the worst times, it would happen at almost every level, every gear and every speed.

I went to our trusted 'house mechanic', but like I mentioned, he was unable to find a solution. At some point the problem went away - completely it seemed. Only to reappear later.

The problem is now presenting itself semi-intermittently in varying degrees. Sometimes it gets pretty bad, sometimes you can hardly notice. It is also possible that in one trip it goes from really bad (like almost not being able to drive) to zero troubles at all.

This problem cannot be good for the engine, so I want to take care of it to make sure it does not further damage the car. If possible, I would like to keep driving this car as I quite liked the car when it was functioning properly.

Additional information on the problem
The jerking seems to be caused my misfires. When accelerating the tachometer will stop and then jump forward, indicating some sort of hesitation.
The problem seems (on average) to be worse in/after wet weather and on colder days. Since the problems have presented semi-intermittently, I have not been able to establish any real connections.

Somehow the problem – on average – also seems to be influenced slightly by how full the gas tank is. It does not seem directly related and it may be more of a gut feeling, but to me it seems that the problem is (on average) aggravated by low fuel levels.

The problem does not seem to be affected by fuel quality (E10/E5), but I have not tested this extensively.

The problem seems to go away after driving for longer periods of time on a highway (>1 hours). This is not always the case, but in general performance seems to be better afterwards.

I think (but I'm not 100% sure) that there may also be some slight power loss overall, but this could just be my imagination after a long time of engine trouble.

Secondary problems (might be related)
Another small issue that may or may not be related to the main problem I’ve been having is that my engine coolant has been leaking since I bought the car. It is a small leak that my mechanic has not been able to find – no even when applying pressure to the circuit – but I have had to top up the coolant reservoir several times in the past year, so there is definitely a leak somewhere. My guess is that this may be somewhere internally (possibly somewhere in the engine?). If this is the case, would it be possible that this leak can cause misfires?

At some point I also had issues with power loss and really slow acceleration. This resulted in error codes related to the turbocharger. These problems have been fixed by replacing the vacuum check valve and this seemed to be a separate issue from the one described above.

I noticed that the start-stop system will not do its job intermittently. It does not seem to be due to colder temperatures, although I haven't ruled that out completely. It is very inconsistent behavior, but it seems that the start stop issues are not related to the main problem; they seem to occur independently.

Diagnostics / fault codes
I have also used an ODB2-device to check if there have been any fault codes. The following codes have been generated at some point:

• P0302(92)
• P0300(92)
• P0301(92)

I noticed that fault codes relating to cylinder 2 occurred more often than codes relating to cylinder 1.

I have also reset these codes on several occasions to check if they would reappear when the problem presents itself again. This was not always the case.

The check engine light is not generally activated when the problem presents itself; it has flashed on only 3 occasions where the jerking become very significant. Other than that I have not noticed the light be turned on, even when a fault code was generated.

What has already been done?
Parts that have been replaced:

• Sparkplugs;
• Ignition coils;
• A part that the mechanic described as the part that controls the turbo; after some googleing it seems to have solenoid in the name;
• Turbo pressure sensor (this could be the MAP sensor)
• Vacuum check valve (this has seemingly solved a problem that occurred later)

I have inspected the MAF sensor and I tried cleaning this with a MAF cleaning spay; this did not have any measurable effect and I did not notice any improvement or deterioration.

I have not been able to spot any loose connections or damage of any kind that could be relevant, but I am not a mechanic, nor do I have much experience with fixing cars.
My mechanic has also checked the gaskets – he did not sport any problems there. In trying to diagnose the issue he must have checked on several other things, but he has not informed me of any other things he checked.

I have tried a gas additive that claims to be efficient in cleaning fuel injectors (Wynn's 55963 Injector Cleaner for Petrol Engines). I have not noticed any improvements or deteriorations as a result.

Using a multimeter I tested the car batteries, and this seems fine.

What to try next?
I am really looking for suggestions as to what I should try next. Based on all the forums I have found regarding problems similar to mine I was thinking that there may be some issue with the catalytic converter. Other potential culprits I have been contemplating are the fuel injectors, the fuel pump, the MAF sensor (or really anything involved in the airflow going into the cylinders).
Does this sound right? Any other potential culprits?

Finally
If any of you have any clue as to what might be causing these issues, please let me know. If I need to do some physical investigating, I am happy to try this. I have basic tools, wrenches, etc. for automobile repairs and can perform basic stuff myself. I don’t have any professional equipment such as hydraulic lifts, so for real heavy duty work, I will need to contact a garage, but this can be arranged.

If you need any additional information, please let me know and I will provide this best I can. Any response is appreciated and I hope one of you has the solution!


Sincerely,
A semi-desperate car owner