OK so I recently purchased a rebuilt 2014 Ford Focus ST3 with about 11,000 miles on it. The engine is a turbocharged 2.0L EcoBoost. I usually use 91 or 93 octane fuel, whichever is the highest available. I love the car - 6 speed manual and around 285 horsepower (with tune) is a lot of fun to drive. When I bought it, I had the mechanic that was rebuilding it put an Injen cold air intake on it. A few weeks after I got the car, I took the it to a local performance shop to get it tuned. The tune works great and added a bit of power to the car, but now I have a strange issue.
About 1 time out of 75 when I take off, the car throttle is limited and displays the message “Engine fault - service engine now”. On one occasion the engine even stalled on me while crossing a highway. Note that this happens while shifting into and releasing the clutch ONLY on first or second gear. In order to get my car running properly again, I need to come to a complete stop and turn off the engine and then restart it. Sometimes the check engine light stays on, but it usually goes away after I restart. The only engine code that is shown is P106B, which has something to do with an incorrect reading on MAF sensor causing the throttle body to close.
Research online told me this issue is commonly caused by a damaged/improperly sealed intake filter or a crack in the intake itself, which changes the angle that air hits the MAF sensor. I have checked both of these and they are good. I have ruled out a bad throttle body control because if that is bad it usually throws another code indicating that it is faulty.
The only thing that I can think of, and I may be wrong, is that when the performance shop tuned my car they tuned it for a stock intake. This would mean that the car does not think it should be getting the airflow that it is and throttles it down to compensate.
I am not sure what to do at this point because (A) the issue impossible to replicate and seems to happen at random, and (B) I cannot just take it to the performance shop and tell them to fix it because I am not sure what is wrong in the first place. Any suggestions/ideas are welcome.