Loosing power and stalling when idle

[SunshinyDays]

Good evening. I would really appreciate some help, I’m new here so sorry to bore you but here goes…my Audi a3 2010 diesel started playing up the other day struggling when going around a round about and when going up hill (jerking and juddering), the next day the same but started to cut out when idle waiting at lights etc, took to a garage to see if possibly fuel filter, they looked at the fuel filter and said looks clean (not sure why they didn’t just change it) plugged it in but no codes except ECU code fault but I’ve had this for ages as it seemed to have thrown this up when we had the battery changed before and then couldn’t map it to work with start stop function, they said it could be an issue with the ECU. Spoke to an ECU remapping guy and he said we could order one and he would remap but just doesn’t think it is this.
Called the AA out as stalled again but managed to get home and he plugged it in to check performance and he said it could be fuel filter but worth changing the housing too, so we changed the fuel filter but not the housing as need to buy aftermarket one and will take a while but still doing it and getting worse. Is it worth changing the fuel filter housing has anyone had a similar problem? 
I just don’t know when to begin with it as if we take to another garage they will charge loads just to look trying to identify the problem before we can even fix it.

Could it be the ECU or fuel filter housing, it could be so many things. 
thank you for reading and sorry if I’ve gone on!! 

[cliffcoggin]

You say the problem started when the battery was changed, but did you code the new battery to the car. If not, that might explain many of the subsequent problems.

I suggest you take the car to an auto electrician for a full diagnosis and hope no permanent damage has been done.

[SunshinyDays]

Hi Cliff thank you for your message I appreciate you taking your time to read. The battery was replaced a couple of years back I believe, it was done at a Halfords auto centre and since they fitted it the start stop function never worked after that and they said they don’t do that there, I was annoyed at the time as wish they had mentioned this before we went ahead with it there and after that I just got used to it and didn’t bother getting it sorted, in hindsight should have done so. 
This problem with the engine cutting off has only been a recent problem so I’m not sure it could be to do with that could it? 

[John6502]

Hi Jessica, I would suggest checking out your MAF s'tensor - when I had an issue with one it did just what you describe - significantly reduction in performance and erratic idling response.

I doubt it's the battery coding issue; the stop/start system just check if the battery is capable of delivering the power without causing excessive voltage drop (if it isn't then it could cause other electronic components to hic-up during the startup which you really wouldn't want) and if it senses a problem it just disables the stop/start system.

Edited December 9 by John6502
added battery coding comment

[cliffcoggin]

12 hours ago, SunshinyDays said:

This problem with the engine cutting off has only been a recent problem so I’m not sure it could be to do with that could it? 

It could be a thousand things Jessica, all of them electrical, so it makes sense to ensure the battery, (which you have thrown doubt on,) is in good condition before embarking on some diagnosis. Don't be tempted to renew components at random, or have the ECU remapped unnecessarily, else you will throw thousands of pounds down the drain.

You have not, or maybe can not, answer my question about whether the battery was coded to the car when it was renewed, hence my suggestion to get it tested as a first step. Once that has been established, get the car tested with a decent code scanner, not a cheap home tool.

[John6502]

Jessica, take a look at this link for the symptons of a bad MAF sensor and count how many apply to your car and then you can decide whether to change it or not:

https://mechanicbase.com/engine/mass-air-flow-sensor-symptoms-maf/

[John6502]

Oh and if you do decide to replace it, don't go for a cheap after market one like I did, yes it gave me back my acceleration  top end performance but it was even harder to start. Changed it for manufacturer's original part and all issues fixed.

[SunshinyDays]

Thank you for your replies, this is very much appreciated 😊

[Anton8]

Hi Jessica

I had exactly this problem with a BMW I had. Lumpy running and cutting out. The problem on this occasion was that when I had topped up the engine oil I had cross threaded the oil cap which allowed air to get into the system. Being a sealed system it was causing the MAF sensor to give incorrect info to the ECU. Just a thought.

Tony