They tend to tear near the throttle body end and on the back-side (where it's hard to see). To check for this start the van and while it's idling grab the tube and squeeze it. If the van stumbles or stalls then the tube is leaking air. A leaking air tube will make the van run bad because the air flow meter needs to monitor ALL the intake air to function correctly.
Here's a picture of a really bad air tube:
Even one that's just barely cracked will make the van run bad......especially when in gear at low RPM or at an idle. This is because the engine torques to the side when it's in gear.........and this sideways torque makes the crack open bigger.............. Tim