There's no electronic control on the 617, so, either the IP curb idle is too high or the linkage is binding.

As Sixto mentioned, disconnect the linkage from the pedal to the IP, as close to the IP as you can, and see if the idle drops down. If not, then make a curb idle adjustment.

The curb idle screw is on the inside of the IP. It's a long screw and is secured at a small protrusion of the IP with a nut. You'll need a long socket to reach it. The danger here is that the nut has not been moved in 20 years. If you put a bunch of torque to it, you can snap off the threaded lug on the IP. It's been done before. So, make sure you spray it down with Kroil or PB for several days before you tackle the job. I always prefer a touch of heat as well. Do not force the locking nut.......whatever you do.

Once the locking nut is loose, you can turn the threaded rod to adjust the idle speed.