For some types of cars, gas octane really does matter, and putting low octane into a car that requires high octane can cause problems. Here's how to fix them.
Accidentally pumping regular 87 octane gas into a car that requires 93 octane may cause the “Check Engine” light to come on. Vehicle computers can compensate for less than optimal octane by reducing ignition timing. But if your owner’s manual recommends 93 octane and you fill it with 87, you can easily exceed the computer’s ability to compensate. So use the correct octane gas the next time you fill up.
In the meantime, to get the check engine light to go off, buy octane booster at the auto parts store. Follow the dosing directions and dump the proper amount into the tank. If the cause of your check engine light is octane related, the booster will fix the problem after about 20 miles of driving.