Tractor Repair: ford 3000 throttle, rubber grommet, friction device

Question
I have a '67 ford 3000, 3 cyl diesel.It idles fine, and runs fine as long as I hold the throttle. If I release the throttle at any speed over idle, it will not hold, but quickly idle back down on its own. Its like the throttle lever is spring loaded or something. I replaced the rubber grommet that holds the lever in the sheet metal by the steering column, but that made no difference.I can't see anything wrong where it connects to the engine. Thanks.

Answer
  There is a friction device under the dash where you probably can't see it.  It either needs adjusting or is worn out.  The rubber grommet is not related to the throttle friction.  To see a breakdown of the throttle parts, go to newholland.com, select parts and services, then select search for parts.  Enter your model in the search box and click search.  Select your model from the results.  You will be able to look up any parts along with the part numbers.