Generaly this problem is caused by vacuum leaks. One common problem area is the throttle plate shaft where it goes through the throttle body. Test by wiggling it for up and down or fron to rear movement or spray starting fluid at that area and see if your idle speed increases indicating a vacuum leak there. Have you tried the idle tube modification? It is described on the YJ board by BillyBadAss. It's a simple mod and allows the carb to compensate for lean running conditions. Try this link for the idle tube mod.:
'87 Wrangler YJ 4.2 I6 (sorry, sold)
2 1/2" ProComp Lift
31" BFG A/T's
Custom Rock Guards
Rear Track Bar in the shed
Other Tricks I won't tell to just anybody!
'99 Grand Cherokee 4.7 V8
ProComp MX6 shocks
Alpine CD with Infinity+iPod connect
Just getting started!
If you're not living on the edge...
you're taking up too much space.