28B8 code

[Jamturbo]

Hi,
I have a strange problem which I have been trying to get to the bottom of. My diagnostic machine says it is related to the mechanical exhaust stiffness, pointing at the vanos solenoid area (28B8). I have replaced both intake and exhaust solenoids. Each time I have checked the solenoids and pistons the car runs perfectly, the rough idle between 700 -800 disappears but after say4-6 weeks the rough idle comes back with the same code.

Fir info, I have also replaced all the ignition coils and sparks.

I have checked the pistons three times now.

I have come across others who have experienced the same but I don't know why it runs well for only a short time.

Thankful for your thoughts

 

[enuff_zed]

M54?
I had the same issue. It was the shuttle valve that the solenoid operates. It sticks.
Pull it out and give it a clean and a rub down with fine wet’n’dry. It is probably sticking slightly in its bore

 

[Jamturbo]

Hi enuff-zed. Yep, M54. I shall give it a fine rub like you suggest. I have only wiped the pistons previously. Thanks again.

 

[enuff_zed]

Hi enuff-zed. Yep, M54. I shall give it a fine rub like you suggest. I have only wiped the pistons previously. Thanks again.

Be careful as the exhaust one points down and you could lose the spring from behind it.