There are several best practices to follow when using precision RF cables and RF connectors. It is important to keep the connectors clean, to avoid distortion of the connectors, and to keep the center conductor of the connector intact.
When the connectors are separated, check for physical damage. The center connector should not be loose and should have no visible dents or scratches. A small magnifying glass will help with this check. Any damage or contamination can cause micro-arc or diode effects to occur, resulting in a certain degree of PIM. This check also helps to discover the source of the VSWR problem.
Keep connectors clean to minimize PIM. This program borrowed from laboratory practice is useful whenever the connector is suspected. Before reassembly, it requires a cotton swab, low pressure air, isopropyl alcohol and a toothpick to clean the connector.