1992 Ford F-250 Custom 8 Cyl 5.0L
The truck runs very rough and will not idle. When I remove the crankcase vent hose from the air filter box it smooths
Some kind of vacuum leak. Leave the vent hose connected. Instead of removing the hose, unscrew the oil fill cap and see if the same thing happens. If the engine smoothes, it doesn't mean you fixed it, it just means that there is a problem with maybe the PCV system - the PCV valve or hose, further diagnostics is necessary to figure out the roughness.