After hearing this problem discussed a hundred times on the list, and recieving a lot of mail, I figured I'd whip up a quick FAQ on what you should look for when you encounter this common problem. 99 times out of 100, it's one of these fixes. Hopefully you're not among the 1% that has to go to the dealer to have them fit one of those UGLY black "kludge boxes" onto your ECU.
1) Block off your EGR valve. Sometimes these fail, and when they do, this is what happens. It happened on my car, then I put in a block-off plate and everything was great. They also cool your intake noticably, and you'll never have to clean your TB ever again! To get one of these great little things, send some email to my mentor, Frank Szymkowski.
2) Change your vaccum hoses, especially the one going to the fuel-pressure regulator. Sometimes this one leaks and creates problems for the FPR.
3) Change your plug wires. I'd use some MagnaCore wires. They're less $$$ than the stock ones, and they're 8.5mm opposed to the stock 6mm. The stock wires are no good, especially when raising the boost.
4) Clean your throttle body REALLY well. Make it spotless, including both sides of the throttle plate.
5) Clean out your intercooler. Do this by taking it out, dump about a gallon of gasoline into it, then shake it around and dump out. Repeat process until gas coming out is clean.
Do all of these, and your car will run better than new!!