I have a 98 JEEP GC 4.0. It started off with rough idle at a stop and stalling here or there. Now it's gotten worse when its warmed up and I stop at a light the idle drops and sounds like it's about to stall. Sounds like I have a knock off cam ha-ha but the my rpm gauge goes ballistic and jumping up to 3grand for a split second but the engine sound doesn't change at all. When I go to drive it pretty much stumbles thru first. Any ideas??

 

Mine did that for a long time and I wasted gobs of money and has. All for a fuel pressure problem. Check your pressure regulator. My problem was intermittent until the damn thing failed altogether, so a pressure check doesn't mean squat, as it can come and go.