Astra faulty injection system

That sounds familiar. I had similar symptoms on my old Peugeot 206, though not quite as pronounced. Check the connection to the mass airflow sensor and inspect the air intake hose for any cracks or leaks. Those can mess with the fuel mixture. How old is your air filter? A clogged one can also cause issues.

Thanks for the advice. The air filter is relatively new. When you mention the mass airflow sensor connection, are you referring to the plug itself, or should I be looking at the wiring further down the line?

I'd start with the plug itself, make sure it's clean and securely connected. Give the wires a gentle wiggle while the engine is running (carefully!) to see if that changes anything. But honestly, given the symptoms and your suspicion of a connection issue, it's probably best to get it properly diagnosed by a workshop. Could save you a lot of time and potential further damage.

Thanks, I appreciate the advice. It turned out to be a defective plug connection, just as suspected. The workshop charged 95€ to diagnose and repair it.