In order to successfully pull off an invasion, a LOT of things would have to have been in Iraq's favor. Saddam could certainly have had better results by holding off on the officer purges, or not putting political officers into each unit to keep an eye out for disloyal behavior, etc. The usual Red Army issues, coupled with not nearly enough numbers.
If we're keeping Saddam in charge of this little expedition, it would have gone much better had Ayatollah Khomeini disbanded the Iranian Army at the insistence of his advisors, trusting in the Revolutionary Guard to loyally handle any threats to the republic. With this done, and an all-in Iraqi blitz into Khuzestan province that expected to actually fight instead of accept flowers from a grateful populace, then there's a *chance* of holding their captured territory until negotiations conclude, or at least beyond the 2 years they did OTL. Mayhap even more support to the Kurds on the Iranian side of the border to help keep them off balance. Anything they do would have to be done FAST in order to set up enough fortifications to hold off the consequent Iranian human-wave counterassaults.
In all, Khuzestan's about as much as we could expect Iraq to conquer, and as mentioned above the stars would really have to align in their favor first.