P0200 Fault on Ford Fiesta 1.4 TDCi - Unstable Idle Especially When Warm

Hi everyone, I'm experiencing a persistent idle issue with my Ford Fiesta 1.4 TDCi engine. The problem is a very lumpy and unstable idle, which becomes significantly worse when the engine is warm. The car has covered approximately 78,000 miles, and the only recurring diagnostic trouble code (DTC) I'm seeing is P0200 — indicating an issue with the fuel injector circuit. Previously, there was also a P02C1FINED error, though I can't identify what it means and it has not returned since. I've already replaced the injectors, cleaned all connectors, and verified voltage to the injectors — everything appears normal. The vehicle starts easily, runs smoothly under load, and shows no visible smoke or performance issues. Despite these checks, the idle remains unstable, and I'm completely stuck on this issue. Any insights or solutions from owners of similar models would be greatly appreciated! Thanks, Pete