Quote Originally Posted by aaronng View Post
Of course. It's a doubled effect when hot.

1st, hot air is less dense, so the engine injects less petrol. Less intake charge means a less powerful combustion.

2nd, when it is hot, your A/C compressor is running for a longer proportion of time to keep the cabin cool. So you would lose power there.
totally agree with aaronng. on both counts,