2000 Windstar LX Starts but Stalls

My van Starts fine but immediately stalls, you can put your foot on the gas and rev it up but if you take your foot off the gas it stalls. You can sometimes rev it up and then put it in gear and then it stalls.
We thought it was something to do with the fuel system so we changed the fuel filter and it is the same. We cleaned the idle air valve and again no change.
We were told that it isn’t likely to be the fuel pump that it will either work or not, so this point any suggestions would be greatly appreciated.
We don’t have the money right now to give up and take it in unless we have no choice.
We also have the common codes 0171 & 0174 with the engine light on and am not sure if they re effecting anything else or not we have had those codes for almost 1 year but when we asked about them we were told they wouldn’t be problem to drive with .
Thank you for Any help.

2001 with the P0171 / 174 is covered in the sticky post at the top of this forum, this link has excellent information and pictures.
http://leckemby.net/windstar/windstar01.html

It is also possible that the IAC is defective and needing replacement.