Man am I interested in the solution to this problem. I have the identical problem in my 1992 22RE engine. I replaced the original dashpot assembly thinking that a burr on the plunger prevented the throttle from returning to the idle stop position. Not so. Problem is still there with new dashpot installed. BTW, the engine seems to run just fine without any dashpot assembly installed (throttle correctly returns to idle stop position)!
Thanks,
James