Porsche-specific: Bank 1 (cylinders 1-3) adaptive fuel trim has reached its maximum limit adding fuel — the mixture is so lean the DME cannot compensate. Note: many forums wrongly call P1128/P1130 separate banks; per PCA both are Bank 1 (P1128 = above limit / too lean).
SYMPTOMS
- Check-engine light
- Rough or lean running
- Hesitation
LIKELY CAUSES
- Damaged or dirty MAF (often after disturbing the air-filter box or using an over-oiled aftermarket filter)
- Vacuum leak
- Low fuel pressure
- Faulty purge valve
DIAGNOSIS STEPS
- Note any recent air-filter service
- Inspect/clean the MAF
- Smoke-test the intake
- Check fuel pressure and purge valve
RELATED PARTS
- MAF sensor
- Intake boots
- Purge valve