Check the routing of your throttle cable in the engine bay, it may be routed wrong, allowing it to rub against something that would cause the vibration, especially if it's rubbed through the rubber coating on the cable.
Just something to look at.
__________________
Huck
Subaru Ambassador
92 SVX LS-Tour Magnaflow Exhaust, 5-Spd-AWD
88 XT6 AWD 5-Speed "Bride of FrankenWedge"
15 Impreza Premium Sedan
15 Crosstrek XV 5-Speed
My 5-Speed "How-To" Write-up
1976 Pontiac Firebird Formula
Current Count of Subaru's Owned.... "70"