The line on the right (passenger) side rocker cover is the crankcase vent line. It is connected to the throttle body upper right port. It supplies filtered fresh air to the crancase so the PCV system can operate. There should be no suction on the line from the throttle body, but there should be a slight vacuum at the hole in teh rocker cover. If you cover the hole in the rocker cover with your thumb while the engine is running, the vacuum should increase gradually if the system is working properly. | 
