2002 Ford Ranger Shaking, Stalling, Check Engine

My truck has started to make a shuddering over the past few days while stopped. This shuddeing doesn't seem to be as much of a problem when the air was turned on. Yesterday the Check Engine light also lit up on the dashboard and it stalled while stopped at a red light (but I was able to restart the engine and keep driving). Does this sound like a simple problem or does it sound like major engine failure? Thank you for your time.