Engine is choking

[Grinder]

Hi all,

I have Boxster S where is 90tkm in the meter (manual transmission).
When i accelerate slowly from the traffic lights it`s sometimes feels like its choking when i put second or third gear. It doesn`t happens all the time but when it happens revs like try to go up but always drops little bit and it does not accelerate anymore. When it happens i have to let go gas pedal or push it to the down. Then its working ok again. I think it happens when engine is idling (like i am waiting on traffic light or in some parking spot engine running.

Any ideas what can cause this?

PS. sorry my bad English..