Help! sentra acting very funny

[duffman1278]

Well the check engine light on my sisters Sentra came on and the OBD II reader says that it is a "p0300 multiple cyclinder misfire detection" According to her and my brother n law the car idles at about 1500RPM when you start the car in the morning. They say that it also shakes at that idle speed for about 30 sec. and than stops shaking, but retains the same high idle. Than when you drive it goes back to normal. PLZ, any suggestions would help. BTW the following was just replaced, CAS and spark plugs. Its an 01 all stock.

[nametakennow]

The high idle sounds like a vac leak. The misfire could be more serious, but without any tools to look at it it's tough to diagnose. You're pretty much stuck taking it to a shop.