My 91 240sx was acting funny this morning. I was just driving down my road and at a low speed. Then all of a sudden it felt like it was missing and when I came to a stop, it acted like it wanted to stall. When I revved it up, it would only go to about 3,000 rpm it's highest and would jump up and down...sort of sounded like a rotary. Also there was a weird smell coming from the exhaust. When I tried to go, the whole car was shaking and the rpm's were going up and down again. The car has been driving fine until today. It's just a stock ka24de 5 speed. I'm not sure what it is. Hoping someone on here can lead me in the right direction. Thanks!