Hi,
if all is as in mid-July, you can always catch the bus in Baramkeh. I was there when the Karaj has moved and the office was left on place. I have read some threads, recents, confirming that you always can take the bus here.
The bus office and stop was 150 m just in front on the entrance on Chari' Filastîn (the former part of the station for the microbuses), just in the corner in front of the entrance.
If you have some time during the day, go to Baramkeh and see by yourself or ask on place (the hotels will advice you to take a taxi...).
The Company is, since 2006, ETIHAD (brown new buses, with a jumping gazel as logo). The fare was 25 SP by person and 25 other for each "big" luggage. There is one bus every 30 minutes (on xxh00 and xxh30), at least since 06h00 am to 12h00 pm (midnight). The fare has maybe a little increased with the price of petrol. There is between 30 and 45 minutes between Baramkeh and the airport, depending og the traffic.
There is also another bus of the same company at Karaj Harasta (norhen bus station), going from there to the airport.
You need to be at the airport at least two hours before your flight. Don't forget to keep on you 200 SP for the departure tax. Take water in town (25 SP) instead in the airport (75 SP).
And, if you can post in return the up-to-date situation, it could be useful. Thanks!