Hi All,
I usually love hanging around these forums trying to solve car problems - now i have one of my own! I'm experiencing occasional hesitation at 1200-1400RPM with light accelerator demand. Ill update this thread with my findings but if anyone has ideas they would be gratefully received!
The problem i've tried to get my head around but here are the symptoms:
- Feels like a sudden flat spot between 1200-1400RPM - not turbo lag
- Can cause the car to surge several times until you drive out of it
- 50%+ accelerator seems to reduce it significantly
- Happens during light throttle only
- Happens also with DTC fully off
- Pretty certain its not the gearbox although it was my first suspicion - happens in-gear in manual mode.
- Seems to happen most when the car is warming up, but not noticeable within the first few minutes of driving. Less noticeable when warm.
- Doesn't feel like transfer box - I've had that before in an F20 and this is more subtle. Tyres are correctly matched and inflated.
Troubleshooting Done:- Cleaned MAF & MAP sensors
- Full DTC Scan - no codes
- The fault happens before the O2 sensors go closed loop (not hot enough) so suggests that should be ok.
- ISTA Diagnostics - MAF Setpoint vs Control, Boost Pressure Leakage test, EGR Valve opening, O2 sensor tests, Manifold Sooting, Swirl flaps -> All tests OK
Thoughts:
EGR - My first thought was a sticking EGR but that doesn't explain why the car would be OK under 1200RPM. The full EGR system is only 1.5 years old. The car pulls just fine from 1000-1200rpm. ISTA checked out fine, but it does operate the EGR quite aggressively - maybe its a fault only at partial duty. Thats the only thing i have to go on as yet!
Next Steps:
Logging - I intend to take the car out later with some logging enabled - especially around Airflow. I need to flag the exact point of the hestitation which may not work in Bimmerlink but ill see what i can get.