I live in Las Vegas, NV and I was driving from the freeway I-95 to the I-15 and whil I was going around 45mph on the merging lane my check engine light goes out. While driving on regular speeds it feels the same. Only when the car is on idle speeds the car feels like it has just a little lag.

when I pulled the code I got code 3 which is the MAP sensor so I bought a MAP sensor and just put it on and still has a code. I tried resetting the ecu and I even changed out my ecu with a spare obd1 ecu I had lying around and still the same code. What can it be?