Hi!

I've a C250 TD, automatic.One day, the car didn't want to start. After about 10 mins of trying it did. The battery is fine, all the basics were checked. Once is starting, then running ok, but when I stop it and leave for 1-2 hours, same happening. The mechanic said it's dropping the fuel and is caused, by some pressure control valve in the immobiliser. I've 3 questions:
1. If it's dropping the fuel, why doesn't while it's running?
2. How could this be related to the immobiliser?
3. Do you have any other idea about the casuse?

Thanks