Hello I have 2007 Versa hatchback standard put 200 miles short of 300,000 on the little car. I pulled the motor and replaced with a salvage yard motor. Got it all back together and she runs well other than the idle is surging from about 14 hundred to 23 hundred in an even manner. Idle air control code p0507 and p0420 catalyst system code both upstream and downstream sensors are replaced properly. The car I pulled the motor from was wrecked from behind and also was an automatic mine is 6 speed. Can anyone throw me a bone here as to a clue to what may be wrong.

can be a bunch of problem the trottle body sensor, accelarator sensor,ignition coil,spark plug,cam sensor, fuel pressure, fuel injector,timing,coolant sensor, pcv system,intake air or vacume leak

I'm wondering if it has to do with the junkyard engine being tuned for an automatic trans and then being retrofitted into a 6MT?