1996 Deville..error messages

[mtcm2004]

Hello..I just bought a '96 Deville about 4 months ago. It has 109,000 miles on it. For some reason, I keep getting the following error messages:

1. Service ride control
2. Service idle system

These come on maybe once a day, if that. Also, my service engine soon light keeps going on and off.

First, what do those messages mean? The car is running fine, I haven't noticed any difference.

Also, my check washer fluid message remains on the dashboard, even though the fluid is full. Could these just be bad sensors?

And my last question, how long do Northstar engines usually last?? (my first Caddy)... thanks!!

MIke