I just bought a 1999 LHS as my first car and i was revving it the other day and noticed that the RPM's when floored only go to around 4,500 and then sputters and doesn't go past that RPM when it redlines @ 7 or 8 thousand. also, when revving there is A LOT of white smoke coming from the exhaust and when the engine is at 4,500rpm and sputtering the white exhaust comes out sputtering in poofs. my father thought it was just a blown head gasket or something. Any ideas on what it could be and if it is serious or minor and how much $ to get repaired?