When I went to start my car this morning the engine revved up to 3500 RPM and stayed there. A few pats of the gas and it dropped to 2500. I tried driving it and even after the engine was warm the idle never dropped below 2500 except when at a stop, with a pat of the gas it would drop to 1500 (sometimes). If I pull hard on the throttle linkage I can get it to drop to a normal speed but as soon as I rev it will not drop back down on its own. I lubricated the linkage and the spring looks fine. I visually inspected all the vacuum lines (all look fine) and tried turning the idle adjustment screw so I could at least drive it to work w/o burning out my clutch but there is still something very wrong. Any ideas on how to diagnose the source of this problem?

The car is an 1989 Accord LX-i (fuel injected) with a 5-speed transmission.