Why does engine only start when cold?

no year no joy, not here.
what size diesel
in what country,
they vary by all that.

Its probably a problem with the water temperature sensor. Also do not rev a cold engine. The engine has a "cold start sequence" which is similar to a choke. When the engine gives a cold signal, the fuel mix is made richer and the timing is changed until the engine warms.

Let the engine warm at the preset factory settings. Sometimes the O2 sensors will cancel the cold start sequence before the water is warm. Racing the engine will warm the O2 sensors too quickly.

Has anyone checked fuel pressure cold and hot ? Check engine light on ?

Is the compressor cutting out? It could be the compressor clutch relay is going bad.

two things to check. First, check the EGR valve to see if it is sticking open. this valve is not activated until the engine is warm. This valve could also have a vacuum leak in its diaphragm so check the valve out thoroughly.

Second, there is an engine coolant temp (ECT) sensor that alerts the engine computer as to when the engine is warmed up. If this sensor is faulty and stuck in the full cold mode, it will tell the computer that the engine is cold even when it is fully warmed. The computer will then use the cold engine fuel schedule which is way too much fuel for a warm engine. The engine will run too rich and sputter. In this condition, the computer will schedule too much fuel for a warm start and the engine will flood. That is why you must wait for it too cool down and "match" the faulty sensor.

Note: the ECT has two wires going to it and is dedicated to informing the engine computer. It has nothing to do with the engine temp gauge on the dash board instrument panel. The sender for the dash gauge has only one wire. The two sensors are easily confused.

Find the cold start switch on the engine. This unit will put more fuel into the engine and set the idle a bit higher for cold starts till warm up then go beck to normal. It appears there is a malfunction in this switch. Replace it, or you can do what I did and put a toggle switch on the power in side of this switch so that you can shut it off after it's a bit warmed up and will stay running. That's all I can imagine would cause your problem on diesel engine.

yes you hit the nail right on the head there,, its the tem sensor playing you up, its telling the car's computer its warm when its still cold and it cuts back the fule like pushing in the choke,,, this causes the engine to miss fire and lack power till its warm change the sensor

Hi, have the same problem with my 1995 legacy gt twin turbo and the problem lyes with the ecu temp switch, it sound's like the ecu thinks the engine needs more fuel to start and run

try changing your egr valve first

check the engine and connect a heater for the engine