1988 truck idle problem

I have a 1988 Toyota Pickup, 2.4L 4cyl. When the engine is accelerated the RPM's go up but when you let off the gas the RPM's don't come down. I troubleshot it through a repair manual and decided it was the Dashpot malfunctioning. I decided this because when I pulled the VT valve off the Dashpot I was able to get the engine to kick down to normal idle after a quick punch of the gas (before nothing would get it down). I adjusted the Dashpot to the point that it did not connect to the throttle, but the engine will not kick down on its own (with out quick rev). Now I'm at a loss. The engine idles good when it is idling.

Thanks for any help
Lyle