1992 jeep cherokee rough idle

Something mechanical, ignition, or fuel.
It can run rough under a load such as in gear and ok in neutral with no load. Have you checked the plugs and dist cap ?

This what I think is happening. Your engine is running rich because the ECM thinks it has too much air and so injects more fuel. When you now introduce air, by taking th e vacuum line off, the fuel mixture is now more balanced. Have you cleaned your MAF sensor? Also make sure your engine coolant is full.

Sounds like timing belt.

possibly dirty fuel injectors. try adding some fuel injector cleaner. best boughtin 3 packs at Walmart, etc.

need to see if one of the fuel injectors are faulty

If the ignition turns on and dies while driving, you might have a clogged idle air control valve. The valve is located in the throtle body, just below the air intake hose. Locate the idle air control valve, un plug the connector, unscrew it (you will need star screw driver) and next clean it using an electronic contact cleaner spray, I use 3M for that. Next, make sure all cleaning liquid inside is gone (it evaporates quickly) and re assemble it. This should solve your problem once for all.

It sounds like its out of time move the distriutor a little bit

I'ts quite possible that your distributor is installed one tooth off and is too far advanced, causing the plug to fire before the intake valves are closed completely. Turn it one tooth counter-clockwise and try it again.

I would start by replacing your automatic air intake and throtle body sensor. Check these 2 things out and let me know.

tepfy