here is all the stuff i've fixed + will fix on my car!
let me tell you a little story about my spark plug adventure...
i was driving home from work one summer evening! when suddenly... my rpms continued dropping and almost stalling my engine when stopped. i actually had to rev the engine while stopped to prevent the engine from stalling on me. that was probably the most stressful drive home (during rush hour too).
onto the fixing part... basically there are 2 different diagnostic routes you can take (i've actually done both ways since i had the same issue with my corolla! i'll cover both here)
your spark plugs and ignition coils keep the car running. the ignition coils transform the battery voltage for the spark plugs, which then ignite the air-fuel mixture (gas yippeee)
so they work with each other to keep your engine up and running! not something you should leave for long!
now, onto diagnosing the issue. if you have a code reader (or know someone who has one), definitely use that instead! in my case, my car is quite old and we didn't have the right code reader. i was too cheap to buy one, so we started troubleshooting. the first thing to look at is the general health of your ignition coils. are they dirty? if they are, try giving them a quick wipe. there may be oil and dirt on them affecting their performance. if the rpms are still dropping from that, take a look at the spark plugs. the spark plugs are directly below the ignition coils in the engine. you can use tubing or something to grab them and pull them out of the engine. you'll be able to see if they're pretty worn down.
the spark plug i pulled out of my civic!
now, if you can't tell physically from looking at each part how good they are, i recommend changing out the spark plugs first. spark plugs on average are cheaper than ignition coils ($10-$20 per spark plug, 4-8 depending on engine size), vs an ignition coil is around $100 each (again, the amount will depend on engine size, although you only may need to replace one). i recommend doing further research before changing each of these out since i'm not a professional, but this is a good starting point if you want to avoid the mechanic or at least figure out what's wrong with your car!
good luck and happy fixing! if i can do it you can too :)
here's where the ignition coils are located :D spark plus are right below it in the engine