It has been a traditional strategic option on the part of an aggressor to launch a surprise attack under the guise of "large scale maneuvers" near a border. This would be an opportune time for Iran to totally queer the deal as far as Iraqi elections, faltering US determination, and an immature Iraqi military, with an incursion in force across the border.
True, but the Iranians are not that stupid. They would be attacking a sovereign nation with all the consequences that that would have. In the long term the Iranians would be the ultimate losers in any such scenario. Their military would be simply reduced in an attrition war and they no it. First to go would be their navy and air force assets and their air defence system.
The Iranians are struggling intensley to keep what mil assets operational as they are. If the current regime in Iran wants to survive then the last thing they would do is invade any part of Iraq