High RPM on PD Engines: Causes & Solutions

Hello,

"I'm experiencing a problem with my Passat TDI-PD engine (KB ATJ, 115 hp). Sometimes, immediately after starting, the engine speed jumps to around 2500-3000 RPM. It runs quite unevenly at that point. After about 5 seconds, the engine then runs normally. Neither VW nor Bosch have been able to provide an explanation, and there are no error codes stored in the diagnostic system. It seems that the problem mainly occurs when the engine is warm or has been running recently. The issue occurs sporadically, about 5 times in the last 2 months."

What could be the cause?

Regards,
Rupert Gschwendtner.

Is the air filter clean?

The coolant temperature sensor should be replaced. Disconnect the sensor and start the engine to see if it still runs at a high RPM.
If yes, replace it; if no, continue searching.

Hello Julian,

Thank you for the tip about the coolant temperature sensor. Actually, that sensor was even stored as a fault code a while ago, but it wasn't linked to the starting problem at the time.
I replaced the sensor, and since then, the engine has started normally every time.

It's possible that the performance fluctuations that occasionally occurred were also caused by this sensor. In any case, I have the impression that these fluctuations have also disappeared.

Best regards,

Rupert.

It might be related. The performance of PD engines is somewhat limited when they are cold. If your engine control unit (ECU) thinks the engine is cold due to incorrect temperature data, it will inevitably result in a loss of power.