Misfiring

Basically, my vehicle is slow to accelerate, vibrates seriously anytime I turn on the A/C however drives smoothly when it's off. I sent to a local maintenance shop for my codes to be read and I received a P0316 - Indicating misfiring at start up. Also, my Check engine light blinks about seven times when I turn my key to the on position, however, disappears when I start the engine. (This blinking observation has disappeared and doesn't show up now). Concerned as I was, I replaced my spark plugs which weren't Soo fouled but changed them regardless. I also sent it for an injector cleaning. I also noticed that my radiator fan keeps blowing at high speeds immediately I turn on the AC, hitherto which it used to run at relatively lower speeds and less noisy than it is now. The major headache for me is sluggish acceleration. I literally have to always shift into sport mode anytime I'm overtaking on a single carriageway. The engine feels heavy and slow to respond. I've tried but the lack of technical support is making diagnosis difficult. Kindly help me with this conundrum.