Glow plug problem Audi A4 TDI

Translated on 03-07-2026, 20:48.

Hello,

"I have an A4 TDI, manufactured in 1998, with 90 horsepower. For the past 3 days, it has been taking a very long time to start when the engine is cold, and the engine speed is elevated, around 1150 RPM. Later, when the operating temperature is reached, the speed decreases. Also, when starting the engine when it's already warm, it glows very briefly, like it used to, and the speed is also normal."
What could have been the cause?

Thank you and greetings.

Enis.

Translated on 03-07-2026, 20:49.

... a faulty temperature sensor.

Translated on 03-07-2026, 20:50.

dieselmartin wrote:

.. a defective temperature sensor.

...or corroded contacts in the sensor connector, or a nearly broken wire in the sensor cable: all of this leads to the problems described, because the reported water temperature is lower than the actual temperature.

Translated on 03-07-2026, 20:50.

Actually, I had the oil changed at ATU on Monday, and when I was installing the underbody cover, I noticed that the cover was pressing on a black cable. I asked the mechanic, and he said it wasn't a problem! The cable is routed towards the bumper. Is that the cable for the temperature sensor? What is the cost of temperature sensors and cables?