N52 - Inconsistent Power Issue

[lachlanvos]

Hi all,

I have a 2009 125i (N52 with 3-stage manifold but detuned from factory) which has had a strange issue since purchase a few months ago. I initially noticed that the car feels down on power, particularly below ~4k, when driving around casually, but after driving along a nice road at higher RPM (and getting lots of heat into it), it seems to gain a lot of power at lower RPM. Then when driving the next day once cooled down, it would return back. I chalked this up to the 125i's detuned map, and decided to try my hand at the 130i map on bimmergeeks, which went successfully.

At first I thought the issue had gone away, but I think this was due to the surprise of having more power overall. However, when I went on a nice drive a few days later, it seemed to pick up heaps more power again, compared to when I had just done the remap. As before, the next day it felt slower again.

INPA pulls no relevant codes, only the 2FA3 from remapping. I have so far tried cleaning and swapping the VANOS solenoids (little to no improvement) and cleaning the MAF sensor (although it looked like in my case it was only a temp sensor, no impact). My next step is to check the DISA valves, although I can't think why temperature would affect their operation. I also want to check the eccentric shaft sensor for oil buildup, and even unplug it to see if it fixes the issue, since I've read it sets the valvetronic to max lift and uses the throttle body instead, so it may narrow it down to either VANOS or valvetronic. I've done some logging with Testo, and from what I can tell the actual values of VANOS and valvetronic match the setpoints pretty well, although valvetronic has some weird lags and odd data occasionally. i can post these logs if people are curious.

One odd thing I did notice from logging is that the coolant temp was sitting around 95c (203F) while at a standstill but dropped to 80c (176F) after a few minutes of driving, which seems low for these engines. It is hot here at the moment, maybe it is keeping the temp low as a result?

Anyone else had a similar issue? Any low-hanging fruit I can try before spending money on replacement bits?

Cheers