Efforts by Iran’s Central Bank to halt the rial’s slide look unlikely to improve the situation and risk undermining the government’s successes in reducing inflation. Tehran’s efforts to spark affordable lending to the private sector are set to be stymied.

The Central Bank of Iran (CBI) is acting to arrest the decline in the value of the Iranian rial which had fallen to record lows of close to $1=IR50,000 on the free market, more than 20% down on its value in...