Wenger's men turned on the style to romp home 7-3 against Newcastle but were woeful 72 hours later in a 1-1 draw with struggling Southampton.
Wenger said: "I find it difficult to analyse the players and to know what they are capable of.
"When you score seven goals in one game and only get an own goal in the next one, of course, it is hard.
"We have good offensive potential but we are not consistent enough. I change my mind whether I need to go into the transfer market from game to game.
"If you look at the Newcastle game, you'd say fantastic but if you look at the Southampton game you can say we need to strengthen our offensive department."