Document: Lack of power during cold starts with 2.5 engine and 01V transmission (Solution)

2.5L TDI engine, 01V automatic transmission.
Lack of power during downhill driving.

Cause:
Due to emission regulations, the necessary amount of fuel injection cannot be delivered when the engine is cold, which prevents it from generating the same torque as a warmed-up engine.
Due to the high viscosity (thickness) of the cold oil, the internal friction losses within the engine, and consequently also within the turbocharger, are very high. This is why the turbocharger exhibits a delayed and sluggish response. As a result, the boost pressure is lower, leading to a delayed and sluggish build-up of engine torque. Once the coolant temperature reaches approximately 20°C, the engine almost achieves its full torque output.For this reason, the automatic transmission incorporates a "softer" torque converter that allows it to compensate for the reduced engine torque during cold descents by using a higher engine speed.
This soft torque converter places minimal load on the engine at low engine speeds (below 2000 RPM), which can give the driver the impression that the engine is revving up without any power being transmitted to the transmission. Only at higher engine speeds (above 2000 RPM) does this soft torque converter demand sufficient torque from the engine during acceleration to provide noticeable drive and power transfer.to receive the gearbox.
Even at moderate load levels, the automatic upshift from first to second gear can occur at an engine speed of approximately 3000 RPM.