Seat Ibiza 6L 1.4 100hp BBZ - Misfiring at idle

Hello everyone,

I have a problem with my brother's car that I can't seem to solve: a Seat Ibiza 6L 1.4 100hp, engine code BBZ, manufactured in 2006.

Symptom:
The engine is running rough at idle. The diagnostic data shows misfires on all four cylinders. Some have more, others have less.
The problem only occurs when the engine is idling. The engine has power, and runs smoothly from approximately 1000 RPM.

Troubleshooting attempts:
- Throttle body cleaned and calibrated.
- The EGR valve has already been replaced, but the engine still vibrates when the vehicle is stopped.
- Purchased and swapped 2 ignition coils -> no change.
- Spark plugs replaced 10,000 km ago.
- Lambda sensor replaced before the catalytic converter.
- Replace lambda sensor after catalytic converter.
- Mass points removed, sanded, and reattached.
- Otherwise, the generator and the battery are new.

After installing the new lambda sensors, the engine idles even more smoothly than before.
In the measurement block, under engine load at idle (target: 10-20%), a value of 22-24% is achieved. As soon as the engine speed is increased to approximately 1000 RPM, the load drops to about 19%, and the engine runs normally.

I'm at my wit's end. Please provide support.
Thank you very much.

Regards,
KANE326

Hello,

What are the lambda adjustment values?

Sure, please provide the text you would like me to translate from German to English. I will provide only the translation, without any explanations.
Okay, I'm ready. Please provide the German text you want me to translate.

Best regards, Rainer.

Both adjustment values are at 0.0%.
The lambda factor is between -7% and -4%. Voltage at 0.44x.

Here are some other things I've noticed:
The dropout detection feature is constantly switching between "enabled" and "disabled."

The intake manifold pressure is between 420-440 mbar (target value 240-420 mbar).

Okay, so the inspection failed. The CO level is much too high! Since I've ruled out the oxygen sensors and I've already replaced the pre-catalytic converter, the main catalytic converter is the next thing to check.

That's probably why the engine control unit is reducing the fuel injection, which is causing the reported jerking.

Greetings.

Have you ever thought about a weasel bite or a false air leak?