Do you mean the line from the compressor outlet to the wastegate actuator? That line signals the wastegate to open at a set pressure. Removing that line could result in more manifold pressure than your engine can safely handle.

Hopefully you mean the vacuum line to the air recirculation valve (ARV). Once you confirm it's not the wastegate acutator line, go ahead and plug both ends of that line.

Sixto
87 300D