Cadillac: 90 deville, e91, rpm

Question
what do codes e91 and e98 means i have a book but they are not listed

Answer
E91 = Park/ Neutral circuit problem.

E98 = High RPM Park/Neutral to drive/reverse shift under ISC control.

CLEAR (erase ALL these codes from the computer and see if they return.

To CLEAR the codes:

Re-enter diagnostics via the OFF and warmer buttons. when you see .7.0 simultaneously push and hold the OFF and HI buttons for 2 seconds and then shut OFF the ignition.

Drive the car and see if any of the codes return as E or EE codes.