Q&A

Good luck, let us know how it all works out with your daughters Diamante.

As you said,these cars have a history of electronic issues.I have a 92 and love it,learned to live with the quirks.I had a similar issue,engine rev.The fix was common,and easy,replace the idle air controller (sometimes called IAC,ISC or stepper motor).It requires loosening the intake air hose and moving it out of the way to access the iac on the rear bottom of the throttle body.Remove the wiring plug and then the two screws (10mm I think)that hold it in place.One can be seen and one can't but you can easily feel it,and replace/reverse procedure.Make sure "o" ring is in place.Then start car and let it sit idling for about ten minutes so it can communicate/update with the cars computer.
You can find IAC at salvage yards/parts recyclers or buy one online from hundreds of places including ebay.