Fast-idling Jetta

I have a 20-year old 1.8l Digifant-injected, manual transmission Jetta that has started to idle at 3,000 RPM (once it has warmed up). I’ve looked through the manual and poked and prodded at various things. I think I’ve ruled out the PCV valve, the idle position screw, the idle stabilizer valve, and the temp sensors; I’ve swapped or disconnected them with no effect. If I do disconnect the blue temp sensor, the idle drops to 1,500 or so. It doesn’t hunt or surge, just sits steady, and has no effect on the driveability. I’m not a “mechanic”, but I have changed its oil, brake pads and rotors, radiator, clutch cable and various belts and hoses, so I can handle a wrench and screwdriver. The car doesn’t owe me a cent at this point, but I’d like to solve this without taking it to a garage, if I can. Thanks for any help!