Need help diagnosing this. Cold idle is smooth. Warm idle is jumpy. Car drives great. Getting 70 mpg average on run from Cardiff to Bangor. If o apply slight touch to accelerator the lumpiness stops. 

On 16/04/2022 at 19:54, JPW2010 said:

Need help diagnosing this. Cold idle is smooth. Warm idle is jumpy. Car drives great. Getting 70 mpg average on run from Cardiff to Bangor. If o apply slight touch to accelerator the lumpiness stops. 

My old 1.6tdi used to do this. Put some good quality fuel in it ie Shell v-power (£20) then rag it to clear out the crap and then run normal shell diesel with every 4th fill up v power. These 1.6tdi's dont like cheap supermarket fuel. Never had an issue after switching. 

 

The rough idle was back in 2015 when I got the car and never was an issue again and I sold it in 2020 and 85k. 

 

BUT dont forget that you have a DPF which will go into regen and that will raise the RPM to 1000 and can cause a jolty idle as a result. You can invest in a cheap OBD2 scanner called Carista which allows you to see the level of soot within the DPF. 

Edited 19 April, 20224 yr by JGrindel

If anyone finds that an engine runs better on different standard DERV then no harm in using that, it is only money after all. 

 

There is no difference really in Shell, Texaco, ESSO, BP, Tesco, Asda, Sainsbury, Morrisons or any other standard Diesel in the UK other than the price per litre.

No higher cetane or special additives or detergents one over another maybe little differences in packages but they are not selling you anything special for a few pence or lots of pence extra a litre. 

 

Likely it is over half the diesel cars in the UK get their fuel from the cheaper filling stations, ie at Supermarkets.

 

Premium Diesel (Shell V-Power) might well have that additional detergent package and no higher cetane rating. 

Edited 19 April, 20224 yr by roottoot

Took it to VWAudi BOSCH specialist for diagnostic. Injectors needed recoding but this has caused diesel knock. Needs new ones apparently.