Hi Guys,

I have a 05 A4 1.8T Convertible that has recently developed rough idling. Additionally the emmissions light has come on and a garage has advised that fault code is saying that the mixture is too lean...

I have replaced all the plugs and also bought a new coil which I have tried on each cylinder but this has not stopped the problem. I am relunctant to just buy a new lambda sensor on a whim due to the cost so thought it best to seek advice on the forums in case there is another possible cause I could try...

Guys any advice on this would be appreciated or anyway of testing my current lambda sensor?

Many Thanks
Mark

 

Post the actual code(s) pulled from your ECU and we can narrow it down.

 

System too lean... is there oil in the coils/plugs? your head gasket might need to be replaced.

 

Hi Guys,

The actual code is P0171 system 2 lean. When I replaced the plugs there was a small amount of clean oil halfway down one of the coils (on the outside) on the engine body but it did look very clean and would put it down to a spillage when topping up!

Hopefully the code about will point to he cause and this ain't a head gasket, the car has only done 42k and is very clean...

Thanks
Mark

 

System too lean usually means that you have a vacuum leak or even a PVC leak...there are many ways to test these leaks just youtube it.

if you are getting too much oil in your coils/plugs then you might want to to replace your head gasket valve cover.

 

Guys,

Just a quick note to let you know that this problem has now been resolved, there was a problem with a one way valve (not sure what it is called) that sits at the back underneath the injectors.

It cost £7.65 from Audi and instantly the problem was resolved.

Mark