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Old July 12th, 2018, 15:10   #7
Veteran Member

Almost all TDI engines will have problems starting if the cranking RPM is not above 250. This is more likely to occur when the engine/starter are heat soaked. Its a function of the starting maps in the ECU. When cold, fuel is injected right from 0rpm. When hot, for emissions reasons, fuel is only injected above 250rpm. Check battery connections, boost the car from a second battery when the problem occurs, if it starts with a boost it may just be a weak battery. Often the starter gets weak with old age as well.

Unplugging the coolant temp sensor when hot will confirm the problem, as the ECU will default to the "cold" map, though this isn't easy to do on a B5.

If you have VCDS check torsion value as well. severely retarded cam timing can cause difficult hot starts.
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