Audi Repair: starting troble, diesel engine cars, motor temperature

Question
i had a A6 TDS model 1998 diesel engine the car start right when the motor temperature is cold, but when the temperature rich normal level of working, if i turn off the engine and re start it it took more than 15 seconds to restart. thank you in advance

Answer
Sounds like perhaps the glow plugs are not being activated when the engine is warm.  Maybe a faulty temperature sensor?  I don't know what the diesel engine uses to set glow plug period at different temperatures.  Not many diesel engine cars in the USA.  Let me know what you find,  Jan