Audi A6: Starting Problems with 2.5 TDI Engine

Hi diesel experts .
I tried to educate myself on the topic.
But all this reading has actually confused me more than before.
My Audi takes forever (after two or three attempts of pre-heating) to start.
After 10 seconds or longer of idling, it starts, and then a large white cloud that smells like diesel comes out of the exhaust.
He shakes himself twice and everything is okay.
"While driving, he only experiences a problem in the fourth gear (automatic transmission). When pressing hard on the accelerator, the engine revs up, but the car doesn't accelerate. This doesn't happen when applying moderate pressure to the gas pedal; it only occurs under full load."
Perhaps someone can help me or just offer some advice. I would appreciate it. Thank you in advance to anyone who helps.
P.S.: Unfortunately, I haven't had the error codes read yet.

If the coolant temperature sensor provides incorrect readings, it can lead to inaccurate calculations of fuel injection and engine speed during startup, resulting in a delayed start. Test: Disconnect the coolant temperature sensor. The engine control unit (ECU) will then assume a temperature of -40°C and allow for maximum glow plug duration. If the engine starts more easily after this, replace the sensor.

If the coolant temperature sensor is reporting incorrect temperatures, it will also calculate and transmit an incorrect torque value to the transmission. This causes the clutches to be engaged too weakly or too strongly, which explains your problem. Unfortunately, you may have already damaged the clutch. In addition to replacing the coolant temperature sensor, the automatic transmission fluid needs to be changed, and possibly even the intermediate clutch (which is probably not worth it).

The coolant temperature sensor is duplicated. So, don't be misled by a correct reading on the instrument cluster. The engine may actually be measuring a different, incorrect temperature.

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It can also be used as a verb, meaning "to gust."

Have the glow plugs been checked and are they all in working order?

Replaced the coolant temperature sensor and everything is working fine now.
Thank you very much for your help!

Ambi wrote:

Coolant temperature sensor replaced and everything is fine.

Thank you for your feedback .

After the clutches have already slipped, I would at least change the automatic transmission fluid (ATF) once.

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It can also be used as a verb, meaning "to gust."