Have the car scanned at most autoparts stores for free.
The black exhaust indicates a rich mixture, this could be from a misfire, or a sensor out of range.
Generally, when you have a hot misfire, but runs OK cold, look at the ignitor (ignition module). Even though it is new, by what you have said, it can still be bad.
You want to get this fixed, because a rich mixture will ruin the convertor.
Wednesday, September 24th, 2008 AT 8:39 AM