2011 Opel Astra J 1.6 A16XER – bogs/hesitates only for first 10–15 sec after cold start
Hi everyone,
I’m trying to diagnose a strange cold-start issue on my 2011 Opel Astra J 1.6 petrol, A16XER, 115 hp.
The problem only happens after the car has been sitting for around 7–8 hours or overnight.
The engine starts normally and will idle on its own, but if I lightly press the accelerator during the first 10–15 seconds, it feels like the engine is choking/bogging down, almost as if the mixture is too rich.
If I simply let it idle for 10–15 seconds, after that it responds to the throttle perfectly normally. The problem does not return for the rest of the day unless the car sits for many hours again.
There are no DTCs / no Check Engine light.
Some live-data observations:
- Cold start begins in Open Loop
- Coolant and intake air temperature readings look reasonable
- Fuel pressure while running is around 400 kPa / 4 bar
- MAP at warm idle is around 29–31 kPa
- MAF at idle is around 3–4 g/s
- LTFT at idle is usually around -9% to -11%
- STFT at warm idle is also sometimes slightly negative
- At around 2500 rpm, LTFT improves significantly to roughly -4 to -5%, with STFT around +1 to +3%
- During normal driving the fuel trims are generally much closer to 0
EVAP purge system:
I completely isolated the EVAP line by plugging the intake manifold connection during a cold start. The symptom was exactly the same, so the purge valve/EVAP system seems unlikely.
MAF:
I also tried a cold start with the MAF disconnected. It did not appear to solve the problem.
