[phil200tdi]

I have been trying to diagnose a fault with my N54.

The car started stumbling/shuddering at high RPM and WOT - No codes were generated.. I replaced all the spark plugs and cleaned the Vanos solenoids (swapping them over on refit) - this seemed to resolve the shuddering.

It seemed better for a week or so, but then I pulled a code for misfire on cylinder 3 started to get cut boost when repeatedly going WOT. I replaced the ignition coil on cylinder 3 and again things seemed much better.

Now the car runs like a champ pulling strongly with/without meth. BUT...
the car still occasionally goes into reduced boost - like 8/9psi. Could this be as a result of air in the meth line and the failsafe kicking in? a minute or so later its good to go!

A few back to back runs like this and switch to map two - I dont usually have so little mechanical sympathy, just trying to trigger a code!! pulls hard through the rev range and then when lifting off I trigger a CEL!

Hopeful of finally pulling a code I Connect laptop and the only thing recorded is:
3100 low boost mode engaged -- CEL displayed

What could be the problem? Other coils, Injectors, fuel pump? Its difficult to diagnose without codes...

[MilehighM3]

Possibly a vacuum leak in the waste gate circuit, or binding/sticking waste gates- aka turbo time

[fastloop]

Any other codes?

Have you checked your vacuum hoses that goes across the engine? Have a look at them and the hoses from the vacuum canisters to the pressure converters. I just changed mine today as a pre-caution. The looked like they had seen better days.

[phil200tdi]

I'll give this a try. Thanks

[WNF_335i]

having the same issue did you resolve your problem?

[phil200tdi]

Changed the vacuum lines, canisters and boost actuators.

Runs well now.

[TVPhoto]

I had the same problem. Is ur car a MT?

[phil200tdi]

Yep