Cutting out when releasing throttle at high speed.

[MTDJAG]

Background:
When driving on highways at higher speed, and then letting up the accelerator for reduced speed, the engine would go down to idle, regardless if the accelerator was pushed. It would run at idle speed for about 20-30 seconds and then it would be possible to push the throttle again and continue to drive.

Solution:
After advice form David Marks, the throttle body was replaced and the fault has never occurred since.