Yes, if the IACV is stuffed, you will need one no matter what. However, like I said, it is possible that it is a AFM problem, even though 98's are less prone to failure then the 99's but it is still possible. I once thought I had an IACV problem but it was something completely different (after market
ecu issue) so best to borrow someone elses IACV for a little while and see if it fixes it. I'm not sure if the MY98 and 99 IACV's are the same, but if they are, then I have a spare you can borrow to test.
Cheers,
Darren