My 05 Passat TDI, 250K, suddenly developed the long crank when warm problem. No problem on cold start, but once it's up to temperature, it takes ten seconds or more to fire. It never didn't fire. It runs fine once it starts. Even after the long crank, it doesn't skip or smoke.
Replaced lift pump, fuel filter, thermo-t. No joy.
Replaced fuel lines with clear lines. Air is visible on the return side,, but only after warm up.
Replaced Tandem pump. Air is still visible, still long crank. Still no joy. No codes. All readings within normal limits.
Conclusion: air is getting in at the injectors because of heat-related expansion. Injector seals?
Am I missing something?