Diesel Pump Diagnosis: Troubleshooting & Repair

Diagnosis: Diesel pump.

I encountered the following problem some time ago.
While driving my Audi A4 TDI V6 with a Tiptronic transmission (year 1999), the engine suddenly stopped and wouldn't restart.
Diagnosis: Error code: 1318.
Control unit for fuel injection pump J399 is defective.

New pump (part number 059 130 106 D) installed, car is working fine.

Now I have another A4 TDI V6 with a 6-speed manual transmission that has the same problem as mentioned above.
However, there's a difference: this car actually runs.
Im Leerlauf ganz normal, aber ohne Leistung während der Fahrt. Maximum speed: 100 km/h.
Going uphill at 30 km/h.

According to Bosch (information subject to confirmation), the car should no longer start if this error occurs and the pump is faulty. There might be another defect, such as a faulty mass airflow sensor (MAF), that is affecting the pump's operation.

Does anyone have any ideas?

"Does anyone know if the fuel pump from an A8 V6 TDI manual transmission (059 130 106 A) is compatible with the aforementioned A4 manual transmission (059 130 106 B)? Both are AFB engines with 150 horsepower."

I've heard that with this engine, the only difference is whether it's a manual or automatic transmission, due to the idle speed setting. But A is not equal to B!