We had exactly the same problem on our 01 Elantra. Took it to the dealer and they repaired it with no problems. This is what they wrote on the invoice, if it helps :
62456 warr hooked up scan pro and found PO507 idle expected to HI. found hole in pvc hose. replaced hose and cleared codes. roadtested and verified repair. the hose wasn't covered on the warranty though, cuz it's a hose!