Welcome to the forums! We'll need to know a bit more about your car to get you goin in the right direction. For a 1998, you could have either an AHU engine, or an ALH. What car do you have? Golf, jetta, New beetle?
Also, just as an FYI, these diesels don't have a throttle valve, and it's been proven over and over again the stock intake ducting is more sufficient than cold air intake on them.