The approach function in my Learjet autopilot has suddenly started acting up and behaving erratically. Sometimes it will pick up the ILS signal from Nav1 as indicated by the green arrow and deviation bar but will not display the distance or knots figures even when only a few miles from the airport and on the runway heading. Most times it will track the localizer but will no longer capture the glideslope. I am intercepting the glideslope from below and at a reasonable speed. Previously when switched to APR and following the localizer it would extinguish the green ALT light when it acquired the glideslope and would ride it down to the runway hands-off. Other odd things are happening with it like the green light on the NAV switch not always extinguishing when I illuminate the HDG switch. I am quite experienced with the Learjet and have only been having these problems in the past day or so. My autopilot problem is unique to the Learjet. I flew a Baron on the same ILS approach that the Learjet flunked and it performed flawlessly. Does anyone have any ideas on what might have gone wrong and how to rectify the problem? I am considering reinstalling FS2004 but wonder if there is a simpler remedy.