2004 1.8t quattro 6speed


during the weekend i changed my engine oil and spark plugs (denso iridium) i notice today while i was on the highway, that my car jerks and the rpm studders above 3 rpm.. any clue why it did that?

Also i need to recharge my ac with the 134a+... i notice two pipe on the top going into the passenger side and the little pipe has a black cap over it.. is that where i charge it from??