(04 Hyundai elantra)I got the car last year for free after it had sat for about 3 years. I jumped it and it fired up after a bit. It was parked due to needing some work one issue being a check engine light for obd readiness. The shop told the previous owner it needed a new cat along with breaks and axles. I put an additive in the fuel to help clean the cat, ran the car, cleared the code it was off for maybe two days and the light came back on this time for a camshaft position sensor. I replaced the sensor and cleared the code but it came back on within a few hours. Any ideas what I should look at to get the code fixed? Thanks.