This can happen if there is a broken tooth on the starter. It can be a broken tooth on the fly wheel but more than likely it is the starter tooth that is broken. Or the starter sylenoid is bad in the starter.
Either the ign. switch is faulty, or the starter is faulty Or the starter solenoid is stuck closed, so the starter is constantly engaged and getting voltage from starter relay. If so you would need to replace the solenoid.
The starter is stuck or apparently engaged, replace the starter to eliminate your problem.
The starter solenoid is sticking or stuck.
If the starter is whining while the engine is running at an idle you have a problem with the ignition switch or the starter solenoid is stuck. The starter should not be engaged while the engine is running unless you are holding the key over on the start position.
The 1991 Ford Explorer should have a separate starter relay that sends power to the starter. It sounds like the relay has stuck and is sending power to the starter even after the vehicle is running.
Could be the bendix in the starter is stuck. all you have to do is tap the starter to get it to release. then try starting it again. If that doesn't work then the starter is probably finished.
Solenoid the starter is stuck would be my suspicion.
just work with it until you get it open. try getting in and kicking from the inside...
how to remove key stuck in ignition switch in Chevy colbalt
Are the battery leads making a tight contact? - checkIs the starter motor stuck? - give it a gentle tap with a hammer.
Solenoid might be stuck. Try tapping it carefully and then try cranking it over.
The starter is stuck.