CEL with p0172 code, rough idle on cold start, 2013 Speed3

Hello, My new to me 13' Speed 3 threw a CEL the day after I bought it, O'Reilly scan showed a p0172 code. Additionally, whenever I cold start the car it idles rough with slight pops, but goes away once the engine warms up.

I drove the car home (1000 miles Phoenix to Denver) after clearing the code and the technician said it shouldn't hurt and I needed to get back home asap for a college exam. CEL only came back on once I stopped for gas the first time 200 ish miles in and turned the car back on, with a slight rough idle that went away. got avg 30mpg over whole drive.

When I told previous owner about it he said it had done it before (though it had thrown a misfire code for him and not the code i have. everything else I described he said was the same though) but he thought it had been fixed, and told me he thought it is most likely a MAF sensor, which he paid to get me direct from Mazda. Just want advice from here on other possible causes or alternatives if it doesn't work or if its obvious its not the issue, i just don't know any better.

Car context:
P.O is a mechanic who bought it with blown engine, put a used engine from a cx-7 in it and has tried to make it as close to as it was from factory has possible. He was very communicative about its condition before the sale and for the most part the car runs great. l'll list the new parts he said he put in it. engine at 59k miles supposedly, odo reads 70k on chassis, hes driven it 5k ish miles since fixing it. funny thing is when technician printed the engine code out the paper listed the mileage at 134k?

No extra power mods or anything like that.

New Parts:
PCV valve
NGK laser iridium spark plugs
LUK flywheel+clutch kit
rear, passenger ,driver motor mounts
Intake +Exhaust manifold gaskets
lower control arms
PCM
Alternator
oem airbox
+ all maintenance

 

Did you ever figure this out?