I drive a Camry 99 model which i bought sometime last year,I travel on Long distance Journey,in which i do not always put on the AC while driving for 4hour Journey,I later found out that anything i tend to use the AC some months back the speed of the car drops.Its takes time to pick up and change,Unless i force the turtle,Before it picks up/moves,It was not like this some last year,This just started a Month ago.

The other problem is when i go for long distance and i check the exhaust pipe at the back i do see black carbon on the exhaust,which i am sure it suppose not to be like that,It should be clean after a long drive,I have been worried about this because ever this has stated i see it takes lot of fuel on long journey which at first it wasn't like that.Any time i am back to Lagos and drive within the exhaust go clean with out any black carbon.Pls i do kindly need help on this.

Hello. Excess fuel is being dumped into the intake. Do you have a check engine light illuminated in your instrument cluster? If you do then first run a diagnostic scan to retrieve malfunction coded stored in the engine control module. This will guide you to the problem area. Further testing will then be required to pin point the issue / issues.
Hope this helps.