Need For Oil During and after the war Iran was struggling with their oil And Russia thought they deserved some of the remaining oil. Due to allies in the cold war the Iranians already owed oil to the US and potentially the Russians but Iran had no oil to distribute. This is and ongoing problem between Iran and Russia.
Terrorism After the war Rebelling groups saw that Iran was Week and started using acts of terrorism to let their voice be spoken. These groups were thought to think that a second war would occur and they did not want that. After the war terrorism sky rocked in Iran.
Nuclear issues The group of Tehran was not getting along with Moscow about buying and using the S-300 missile. Moscow wants Iran to be defenseless to be able to manipulate them.
Iran's disputes over land Iran and Russia had problems over land disputes including over the lands around the Oil. Russia took some land from Iran and now Iran is trying to win it back but Russia is holding a big grudge. Russia claimed the land during the WW's and Iran will not just let them stay but Russia will not yield the land back.
Russia is a threat The Russians and Iranians hated each other over a 5 year war and eventually ended with the two sides holding each other accountable. And Iran's Oil revenues went through the roof because the shortage of Oil. Iran and Russia had their differences but they but had their individual struggles from the cold war.