I just replaced my idler pulley. I spent one day running between parts stores just to find the same: The one referenced for the 1999 Vehicross has the ID too big, and the pulley is made of a flimsy plastic.

At Autozone they seem to have one with a smaller ID for the 2001 model, but I couldn't try it because they (nor any other parts store visited for that matter) didn't have it in stock, and it'd take 3-4 days for them to get it.

I decided to buy the original pulley from St. Charles Isuzu @ $77.31 shipping included. Granted, is waaaay more expensive than those from the parts stores, but it features an all-metal pulley, it comes will all the hardware including metal cover plate, bolt, spacer, and washer, and it has the right ID.

As many said before, when it comes to our beloved VX you can't beat using original parts.