I'm sure I'm going to sound really silly asking this but hear me out lol..
I have a 99 Civic LX, 245k miles on it, Automatic, base model of motor all that stuff.
As of a month ago, my check engine light went on and the code was for a O2 Sensor. Right before I was about to change it( about a week prior) my car started randomly stalling. It didn't matter if it was at a stop, going 35, or on the interstate going 70, it just randomly stalls.. So I changed the oil, and while putting the O2 Sensor on, I found a 6inch crack in my Exhaust Manifold so I changed that. Even after changing it, it still stalled. So I checked the Alternator and fuel filter. I changed both. Now, my car still stalls. I've done a tune up since as well.. After more research, I learned my car had a recall on the ignition switch back in 2002 so I bought a new switch yesterday even tho a new one was put on in 2003 after the recall.. I have a new battery and truly don't know what else the problem could be! Does anyone have any ideas or should I just take it to the mechanic even tho I just spent nearly $700 in parts? I know it all needed to get done anyways but I don't know what to do anymore!! Thankyou in advance =/

 

When it stalls, don't touch the key until you look at the dash and see if the oil and battery lights have come on. They should light up any time the key is on but engine is not turning. If the lights don't come on, it is probably the key switch. If they do it could be the ignition module, which is another major cause of random stalling.