2001 s40, just changed the fuel pressure regulator. Car won't start unless you give it gas and then it dies as soon as I take my foot off the gas.

 

The device shown below is your IAC/idle motor/air bypass valve - whatever you want to call it. I have replaced many bad ones on the s40s because - the engine won't idle. Yours might be bad. (could also be an air leak or some other problem)