2011 Audi a4 problem
 

I had this problem for a month now where I drive my audi 10-15 min to a destination and it works fine. What I have noticed is that when I drive it for more than 30 min it starts to decelerate like the motor brakes it a bit(you can feel a push back a bit) but only happens when i stop pressing on the gas. Another symptom is when im at a stop the car shakes. Lastly when i get home turn off the car and try to turn it back on the only way to turn it back on is if I press the gas. I tightened the air inflow tube screw and it turned on just fine. Im wondering if that did the trick or im just kidding myself. Thank you for time and responses. There is no check engine light on.