how do i make a new ignition key from blank
You need a VATS key, not a standard blank or transponder blank. (http://www.vatskey.com/) You have to determine the correct value VATS key you need using an ohmmeter. Once you have the correct VATS key, cut the blank as you would any key. FYI, sometimes problems with VATS keys are actually in the ignition cylinder itself, with the two leads that should touch the key. Those leads can wear down. If that is the case, the key may be fine but the cylinder has to be replaced. (You would need to replace cylinder and buy matching keys for new cylinder).
Search Oldsmobile Ninety-Eight Questions
Oldsmobile Ninety-Eight Experts