Q: Check Engine light on. Would the computer give all error codes in one shot? How do we know the engine's condition?

Hi, I bought an 05 Kia Sedona having 57k miles, Seller (Tom) posted this one in craigslist, I checked carfax for this van, there are 5 previous owners and it seemed van was not used last 2 years. after I bought CV Shaft assembly on driver side have to be replaced in two weeks, due to huge noise coming on driver side. After I did this repair Check Engine light on, giving the code for Throttle position sensor. Then I doubted the engine and opened engine cover. Found a 2003 kia sedona engine written on it, no indication of how many miles on that engine, seems like he got this engine from junk yard. Seller is not responding to my calls or messages. I am wondering if I replace this sensor, would this engine be giving another error code for something else! I would like to know if there is any problem(s) with engine, would computer gives all error codes in one shot or it will give one after the other after each fix? I would like to know if it is possible to know condition of the engine.

My car has 57000 miles.
My car has an automatic transmission.