Rpm's on my manual transmission 2000 Jetta dip when clutch is engaged.?

Here's some more details. Whenever I put the clutch in, or when i start the car, and the transmission is going down from higher to right around idle, they dip too low and then shoot back up to where they're suppose to be when the engine is idling. When that happens the engine acts as if its going to die for a second until the rpms kick back up. I don't really know what to look for or anything I could do to help this, so any suggestions will help!