Sounds like a intake air leak.
Check the entire intake system. All hoses, Tubes and connections.
If it is the throttle when it is warmed up go to the back, pop the
lid and play with the linkage, If no change that one is out the door.
C-ya Jonce

>Has anyone had this problem?  After my engine reaches operating temp and is
>in stop and go traffic, it doesn't fall back down to idle after I accelerate
>to move forward in traffic.  It just stays revved at 3,000 rpm or
>thereabouts.  Not fun when stuck in traffic.  I'm thinking it has something
>to do with the spring on the throttle (maybe needs to be cleaned or
>greased?).   I haven't worked on this part of the van yet, so I'm not
>familiar with how the accelerator cable hooks up and works in the engine
>compartment.
>
>Thanks for any insights!
>
>Mark
>
>--
>Mark
>1990 Westy (2.1 - manual)