Golf 3 TDI, 1994, keeps stalling

Hello, I'm having the following problem:

My Golf3 90hp TDI, manufactured in 1994, with immobilizer and alarm system, and approximately 260,000 km on the odometer, suddenly stalls while driving.
It usually occurs within the first 5 minutes after starting the engine and happens only once during a trip. A restart is sometimes possible immediately, but sometimes it takes up to 5 minutes. When I try to restart, all the indicator lights are off, and the turn signals activate the parking lights even though the ignition key is in the "on" position. In this state, the starter motor can be engaged, but the engine does not start. It seems like class 15 is missing.
I've already replaced the ignition switch and relay 109, but that didn't solve the problem.

Does anyone have any other advice? I am grateful for any help!
Best regards, Kroste.

Welcome here! Search function rocks!

Please search for "DWA" or "Diebstahlwarnanlage". Then you can find a relevant post ("1Z Golf occasionally stalls").

Maybe this will help...

Regards,
Guste.