City beat Leeds United 3-2 last weekend before Tuesday's 5-4 win at Fulham, where Guardiola's men conceded three goals within 21 minutes after taking a four-goal lead.
"How many shots on target had Leeds? Three and they scored two. Fulham. Five? Six? So the average of what they shoot and we concede is high. We have to improve, of course we have to improve," Guardiola told reporters on Friday.
"All the goals were (from) the edge and we didn't have players there to defend. We will talk... I don't like to concede six goals in two games but we are the team who scored the most and we have to build from that."
City have scored a league-high 32 goals, with forward Erling Haaland leading the scoring charts with 15. But they have conceded 16 goals, more than any other team in the top six.
"We have to fix these kind of things but not lose what we are... we have to be more solid," Guardiola added.
Guardiola said sixth-placed Sunderland, who beat Chelsea and played out competitive draws with Arsenal and Liverpool, will be a challenge.
Promoted Sunderland have lost only one of their last seven matches.
"All I can say, in my humble opinion, they deserve where they are," the manager said.
"When you play newly promoted, three games, four games, five games, OK, momentum. It can happen. But 14 fixtures in the Premier League to take results and be in that position, they deserve it. A good challenge for us."
