S40: S40 2.0t Fault code, Running Lean on bank 1 Help!

[Kaosiow]

So I've just bought the above car, took for a test drive, all was fine.
Driving home and the car just would not go, juddering on acceleration and the emission light came on. Checked the code and it says, Running Lean on Bank 1, a quick Google hasn't really helped, I've checked the Maf by unplugging it and there's no change.

What should I check next?

Thanks in advance. I'm Kirk by the way 😁

[clarkey1984]

The first thing that springs to mind to check for would be a vacuum leak or a dodgy o2 sensor, both of those things would give you a lean condition, the bank 1 part doesn't narrow it down with an inline engine as it obviously only has one bank to begin with, fuel pressure regulator or pump could also be a contender, as could dirty injectors as well, as a rule of thumb I always start with the cheapest part that it could be first, I'm from the budget (read cheap b@st@rd) school of motoring haha.

[Kaosiow]

Going to check the injectors in the morning, and hoses, are there any prone to leaking?

[SIAMBLUE]

I would check plugs and leads first then look at the condition of the plugs when they come out, dirty or wet plugs, from then I would start with the injectors.

[KBB]

Get you scan tool in live data and look at STFT. If STFT is showing a positive number at idle but backs off when held steady at 2500 RPM then I would be looking at an air leak.

If the trims are heavily negative at idle but then go quickly positive at part and full load then suspect MAF as a contaminated MAF will over estimate engine load at idle and under estimate it at load. Further test should be done to confirm this out come.

If the above test is good but under engine load the trims go from normal to positive then a weak fuel pump is a possible, further tests including pressure and volumetric flow should be tested next along with an electrical evaluation of current of the supply and ground to eliminate voltage drops.

If the are no movement in any of the STFT or LTFT values and the scanner is indicating open loop, in live data check the Upstream O2 Sensor PID and check for switching, no switching the are further simple tests that can be done such as forced rich and lean testing to confirm O2 sensor functionality.