Positive Crankcase Ventilation (PCV)
WARNING: This page is about a different car, the 1996 Suzuki Swift. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect hose from PCV valve. Start engine and let idle. Check for vacuum at PCV valve. If vacuum is not present, remove PCV valve from intake manifold. If engine runs rough or stalls, replace PCV valve. If engine does not run rough or stall, check for restriction in PCV valve intake passage. Repair as necessary.