Won't start when cold - 1985 Jaguar XJ6

Hello wyatt...... Is your jag.built with a carburetor or fuel injected?
Carb, your choke is not set to close when cold, and should be set. When set, it also sets a cam that keeps the engine running fast. Then when warm, you hit the pedal and the cam moves, and the engine speed goes to normal. Unless the choke is set, the engine cannot keep running, as it tries to run on cold gas and it can't run good on cold gas. It needs more gas, therefore, and the choke makes more gas go into the engine.

Fuel Injected, the computer should adjust the amount of gas your car is getting when cold. If not, the coolant sensor might be bad.
The coolant sensor senses the cold engine and tells the computer to add more gas. Once the engine is warm, the coolant sensor tells the computer to put the gas to normal.
So, if the sensor is not working, the engine will try to run normal, and if cold, it can't. Joe Thanks for choosing Fixya!

Cold start fuel injector, it only runs 12 seconds then the collant sensor takes over