Hyundai Repair: Hyundai Accent 1998 3dr standard, stalling, hyundai accent, crank sensor

Question
I have a 3-door standard 1998 Hyundai Accent (GS i think) and recently my car started stalling when idling in traffic or at a light. Then it won't start for a couple minutes. The engine will turn but won't start. Then its just like it "decides" to start again.  The check engine will sometimes come on after this and stay on for about a day then goes off. The check engine code says it's the oxygen sensor, but I thought an oxygen sensor wouldn't prevent the car from starting. When idling the engine doesn't run completely smooth, but rather with an intermittent vibration, like the rpm is dipping slightly every second or so. I noticed that if I touch the gas lightly when stopped, the rpm goes up a bit (just below 1000rpm), and the car runs perfectly smooth and this seems to keep the car from stalling, any ideas what this could be? fuel pump? fuel filter? i took it to a mechanic but he said he couldnt get it to stall and would have to spend alot of time checking it out to find the problem. Thank you

-Shawn

Answer
I agree that the oxygen sensor is probably not the problem with the stalling unless you've got an exhaust leak prior to the oxygen sensor.  If that's the case, you should repair the exhaust leak and see if the problem goes away.

I'd suspect you might have an intermittent crank sensor or a faulty idle actuator.  But the mechanic is correct that it'll be difficult to prove what the problem is unless it's occurring.  It's possible that no matter how much checking is done that the mechanic won't be able to find the problem while it's not occurring.