Porter Preheating Lamp and Smoke Issue

Sounds like a dodgy glow control unit. Those symptoms are pretty classic. Have you tried wiggling the wires and plug connected to the unit while the engine is running to see if anything changes? If the light flickers or the engine stumbles, that's a pretty good sign of a bad connection. But with the engine light on, there will definitely be an error code stored. Do you have a code reader to check the error code?

Thanks for the quick response! I haven't tried wiggling the wires yet, but that's a great idea and I'll give it a shot tomorrow. I don't have a code reader myself, but is it worth buying one, or would it be better to just take it to someone who has one? Any recommendations on a decent, affordable code reader, or should I just bite the bullet and go to a workshop?

Honestly, for a one-time thing, unless you're planning on doing more work on your car yourself, it's probably cheaper to just get the code read at a workshop. They'll be able to tell you exactly what's going on. Given the symptoms and your suspicions, it’s almost certainly a faulty glow plug control unit or wiring problem. But without knowing the exact code, it's hard to be 100% sure. Either way, I'd recommend getting it checked out soon, especially with the smoke issue.

Thanks a lot for your help! I wiggled the wires like you suggested, and nothing changed, so I took your advice and went to a workshop. Turns out it was indeed the glow control unit, and the final repair cost came to 95€. Appreciate your advice!