I just bought a 1999 RT-10 with 18,000 miles and no mods. It only has a free flowing exhaust. The engine runs sometimes at 400 rpm and then 1,500 rpm. There is never a happy medium. It also doesn't like to just sit and idle. Is this normal? Also my speaker in the middle between the 2 seats is not loud and full of base. Do these cars just have a bad system in them or is my speaker bad? Thanks, Randy.