1989 LeSabre error code 48

My '89 LeSabre has begun idling high when in Park, but as soon as I put it in gear (Drive or Reverse, doesn't matter), the idle drops down. The error code is a 48, which I can't find in the code charts. Anyone else had this happen & can point me in the right direction? BTW, it's also been giving a code 63 for a while now, which has to do with the cruise control. Since the cruise doesn't work on this car anyway, I've ignored the error, but if it's something that's a quick fix I'd appreciate any advice on that one too.

I can't find a code 48 either.....sure you have the right code?

63 shows up as an EGR problem.....

Code 48
4 flashes, pause 8 flashes
Misfire Diagnosis. Check the ignition and fuel systems.

The older model ECM cannot detect individual misfires, only the units responsible for firing. You could have a problem with the cam sensor, crank sensor, ICM, coils, or associated wiring.