Petrol 1.4 AUA - engine shaking at idle and under light acceleration

[Sylvester]

I have finally managed to do another compression test and it is all ok. That was a big relief.
Anyway I am running injector cleaner now and I will see how it will go.

Hi Mtl, any chance you got a youtube video about how to do the compression test? Cheers

 

[mtl]

No, but is easy if you have the equipment. Take out the spark plugs and push in the compression test device . Engine must be over 80 degrees Celsius. When doing the compression test, throttle needs to be fully pressed.
I was looking at cheap devices (30 EUR), but after reading feedbacks I just went to VW dealer to make the measurement with proper device. I got also this nice little printout.

 

[Mark Adams]

I had some time and checked a few things. Sadly I was not able to do compression test, because I was not able to find mechanic with the tools .
Anyway, in a 30km drive the engine had 1 misfire in cylinder 4 and 7 misfires in cylinder 1. But misfires have not appeared when the engine was not pulling, but when I was coasting for cca. 30 seconds, so the engine was at idle.
Also I did not feel any problems with uneven running when the engine was cold.
I have checked the spark plugs and they look good to me.
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Can these symptoms be because of a problem with injectors? So, no problem with engine when cold and for example when I turn the ACC on, the shaking in idle disappers, since the idle is a little bit higher.
I was checking also some other data and there was a problem with the air intake temperature which was showing around 45 degrees, but I have checked on the similar car and it was the same, it looks like the heat from the engine elevates the reading.
One strange thing was also catalyst temperature which was showing around 150 degrees, which is according to my info, very low. Sadly I did not have more time to investigate into this.
Anyway, to recap: spark plugs replaced, fuel filter replaced, throttle body cleaned and adapted, ignition coil replaced, ignition cables replaced. Remain injectors and maybe cat temp sensor. Is anything else possible to cause these symptoms?

Spark plugs with different appearances are a good sign that there may be injector issues here. Our speciality is Rover V8 engines, which are notorious for these problems with the original beastly Lucas injector (designed down to a price, not up to a standard).

The bit we are interested in is the white ceramic insulator around the central electrode. Assuming that the engine is mechanically sound, then all the plugs should look the same. There should be a uniform coating of very fine grey powdery deposits on the insulator, which may be brownish or pinkish instead if using a premium fuel (such as Shell V-Power or BP Ultimate for example).

A very clean insulator usually indicates that it is being hit by large droplets of poorly-atomised fuel, which literally scours them clean.

Interestingly the mixture will appear lean on any affected cylinder, because although the correct amount of fuel is injected, it burns slowly and incompletely leading to elevated Oxygen and Hydrocarbon levels in the exhaust. Fuel droplets burn from the outside in, therefore the smaller they are, the quicker and more completely they burn.

This is an issue we had with our own AUA engine, which actually turned out to have two Bosch injectors and two Weber Pico injectors when we bought it. The injectors were tested in the ASNU cleaning machine, and indeed there were both spray pattern and flow rate issues. When ultrasonically cleaned, the Weber Pico injectors turned out to have the better spray pattern and atomisation, so we got two more of those and cleaned them up to enable us to fit a matched set of four.

Our 155K Miles AUA now runs beautifully, so well worth doing anyway.

 

[mtl]

I agree, I have this planned in the future, but sadly currently I just don't have time to get this work done. It will need to wait.
Anyway, injector cleaner did not help, hesitation in acceleration is still present. So, next stop definitelly injector testing and ultrasonic cleaning. I really hope that this will solve the issue, because if not, I am out of ideas.

 

[Mark Adams]

I agree, I have this planned in the future, but sadly currently I just don't have time to get this work done. It will need to wait.
Anyway, injector cleaner did not help, hesitation in acceleration is still present. So, next stop definitelly injector testing and ultrasonic cleaning. I really hope that this will solve the issue, because if not, I am out of ideas.

You've helped me far more than you know, with your excelllent how-to videos. I'm just wondering how I can return the favour...

 

[mtl]

You've helped me far more than you know, with your excelllent how-to videos. I'm just wondering how I can return the favour...

No need. The reason to make them is exactly that, so it will help all owners to keep their A2s on the road. If my videos helped you, that is enough for me . This is also my way to give back to this excellent community, without which my A2 would not be on in my ownership anymore ...