it seems be when driving normal. The last time it did it i drove a good ways and had to go up a good hill with the ac on and of course didnt have good power so pushed the gas on to get more speed. Once i got over the hill had a small hill to go up and it started in middle of that hill. Wasnt giving much gas for that hill. When it started a black puff of smoke came out the exhaust. I have taken to garge and them put it on computer but is reading control module or misfire. I am going today to auto zone for them to put in on computer and get the code for sure