My car has a problem and I'm not sure where to turn. I have only had the car for two months so I do not know what to do.

I have the 1995 c280 that was doing great and this weekend when my children and I were out of town, it started acting up. It idles poorly at stops bouncing around quite a bit and then is slow to get away from a stop, back fires once in a while...just no power, feelslike not getting gas. Once I'm up in gears, it does better but does not seem to have full power. Runs better if air conditioning is off, but not much better. I made an emergency stop at a mechanic on the trip. He Changed the spark plugs, the fuel filter, and made sure the battery was full of fluid. Then he found the engine harness to have wires touching and overheating to where the cover was burnt off. He covered the wires the best he could...I have photos of the prior damage. I only have 80,000 miles on this car. This part you would think, would be designed to withstand the heat. It did not wear out from being old...it wore out from heat!
I would appreciate any assistance...Thank you.