The Japanese government on Thursday conducted on-site inspections of two plants of a subsidiary of IHI Corp., a day after the leading engine maker said fuel efficiency data had been falsified for decades. IHI Power System Co.’s plants in Niigata and Gunma prefectures were inspected, the transport ministry said, after data was found to have been rigged for 4,361 engines. IHI said data falsification may have taken place since the late 1980s at the Niigata plant and since 2001 at the Gunma factory. “We will sincerely cooperate and respond. We will make efforts to prevent a recurrence, while seeki…