The brake pedal on my Toyota Landcruiser, 3.0-litre diesel automatic goes down nearly to the floor when driving, although it does stop the vehicle.

I have bled the system to no avail; however, when stationary and in park, when I pump the pedal to remove the servo assist air, the pedal is solid, with no movement. But when I start up, the pedal goes slowly down almost to the floor. If you pump it up, it holds for a split second then goes down.

Any advice? It does not appear to have a brake boost incorporated, only the standard servo and anti-lock fitted. It has covered less than 15,000 miles from new.