Probably need a new intermittent wiper delay module. You can get them from eBay for about $25 or $30 or so.
They're located down by your left knee, usually Velcro'd. Do a search on here... It's a pretty common repair. In fact, I have one on order now and need to do it too once it comes in.
'89 YJ Sahara
4" lift, sitting on 33's, winch, light bar
(hoping to do an 8.8 swap one of these days)