2004 Sunfire stumbles while throttling

I live in in Germany and own a 04 Sunfire with 2.2 Ecotec . The car runs fine, only when I throttle the engine stumbles/stutters (I dont know how to explain it well). I already changed the air filter, but when accelerating there is no problem, only when taking away the gas. I fear that it could be something with the electronics, because here in Germany there is nothing of service resp. Pontiac....
Thanks for all advices !
Felix

change your fuel filter as well

hi, ok I will do this. But I don't understand, why. While accelerating it seems that it gets enough fuel, why it stumbles when throtteling ??
Regards
Felix

Have seen issues like this from dirty injectors, MAF sensors that got dirty to name a couple.