Throttle hang up

[schnowz]

My throttle keeps hanging at 3,000 rpm and will normally return to idle after about 5 secs, The time varies though -sometimes longer. I did check for an air leak in the intake area (WD-40) but couldn't come up with anything conclusive. Took a trip up to New Hampshire last weekend to check out the fall colors and it was a little unnerving having zero engine braking going into a corner  -had to constantly hit the brakes.
Any suggestions on what to check out. I havent tried spraying the hoses under the tank yet. The severity is getting worse and varies and it will sometimes come down if I blip the throttle -
I'm hoping its not a diaphragm issue.
Any thoughts welcome
Pete S