1996 Oldsmobile Aurora P1645

The code: P1645, is the circuit which controls a valve that opens and closes on your "EVAP" canister. This is an emission control device and will not cause a misfire, or any driveability problems.

Now, are you sure that it's only misfiring in the No. 1 cylinder. Just because you have spark at idle, doesn't mean the plug won't misfire under load and high engine speeds.

If this same cylinder is still misfiring, then it could be the one of the ignition coils, or a fuel injector is clogged/faulty. There's no way for you to check these items yourself. You'll have to take the vehicle in.

Also, you won't pass an emissions test with your code: P 1645 showing. That circuit will have to be traced by someone who has competent electrical skills. Because this can be in the wiring, connector, or the solenoid itself.