I bought a 2002 Hyundai Elantra GT last December with about 113,500 miles. Since then I have put on about 500 miles, replaced an alternator, spark plugs, brake pads, an upstream oxygen sensor, and cleaned the fuel filter. The oxygen sensor was replaced about a month ago, it is a universal no name brand (all I could get in Nicaragua, where I live). After a week or two I noticed that the same problem was happening as before the OS replacement - lack of acceleration with my foot on the gas (more so in the city than on the highway), driving along just fine and then… nothing. I would have to pull over and coast until it kicked back in. I’ve been doing my online research and am wondering if generic parts are really that bad and that I should replace with a brand like Bosch, AND replace both the upstream and downstream at the same time, OR could it be something else (fuel pump?)?
I’ve used universal 02 sensors with no problems. What gave you an indication it was the 02 sensor? Was the CEL on? If so what were the codes? The downstream 02 sensor’s only function is to determine whether the catalytic converter is doing it’s job or not and has nothing to do with air/fuel ratio’s or the way the car runs. If the CEL is on have the codes pulled from the ECU and post them that will give us a better indication of what your problem may be. Sometimes a dirty MAF sensor can cause problems like you are describing.
Hyundai?? Nicaragua?? You can’t be serious…Find yourself a stick-shift Toyota or Nissan pick-up like everyone else…
Check air filter and replace not clean fuel filter!
if you can pull codes, definitely try to do that; it’ll save you a lot of guess work. Agree that it probably isn’t your o2 sensor, assuming you spliced it carefully and the wire lengths are the same as the OEM you replaced. In the meantime, when it happens again try to pull over and test for spark and also see if you have any fuel at the injector rail (remove the cap and depress the Schrader valve with the end of your key - should get a nice spray of fuel). As was already mentioned, could be several things, but if you can narrow it down to fuel or spark and find a code reader to borrow, should be pretty easy to figure out.
Also, not sure why you got the negative comment on your choice of a Hyundai; there are tons of Hyundais in Nicaragua these days (its not 1989 anymore) and they are pretty solid used cars. Much more affordable than the JDM import alternatives in NICA as well. Good luck, keep eliminating possibilities and have a cold Presidente for me too when you get it figured out.
Any chance it is water in the fuel tank? Do they sell HEET or equivalent in Nicaragua? Doesn’t hurt to give that a try.
I appreciate all the comments, thank you. I am not the one doing the actual repair, just the research. I watched the “mechanic” use the computer to test the electrical system but didn’t ask him for codes. I will have him test it, again, and I’ll check a few of those other things. It’s a challenge to diagnose a car. It’s an even bigger challenge to diagnose a car in another language AND in a country that lacks the most basic resources.
And, yes, Hyundais, and even KIAs, are everywhere down here. A Toyota would be nice but I no longer have an American salary. I think Presidente is Dominican, but I’ve already had a few cold Toñas! 
Make mine a Salva Vida!
Guess a Coca-Cola will work for me. I think their world wide. Yes definitely try to find out what code(s) it’s throwing and post them.