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ICP = Injection Control Pressure, but you can ignore that. I was trying to go from memory thinking 1247 was an ICP code. Turns out it's a turbo boost low pressure code. I really should look some of these up before I open my big mouth.
If you can't find a boost leak, check the MAP hose and sensor as Robin suggested.
Also, you might want to thumb around through this link 2001 PC/ED Manual
Section 4A has a listing for Diagnostic Trouble Codes and the troubleshooting chart associated with each code.