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Ford Focus ST Throttle Issues

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.

Does this cold-air-intake kit include an air filter that requires oiling?



This is a GTDI Focus. It does not use a MAF, it does have a MAP however. For the most part all EcoBoosts are of a speed density engine management type. The sensor you see next to the airfilter should only be the IAT. Please recheck your DTC… Are you sure you don’t mean P061B and not P106B?

This vintage car was know to have Signal return faults due to wiring harness splice issues… Not saying go after wiring yet but you may want to let it idle and wiggle test the engine harness. Typical harness issues are near the transmission within the harness convolute.

If you do have an MAF sensor, any non-OEM changes to the intake path could change the air flow pattern prior to the sensor and cause this problem. MAP’s aren’t quite as sensitive to the air flow patterns but even then this could be due to the changes in the intake air path. Suggest to return the car to the OEM configuration as a diagnostic. If it runs well and without this problem in the OEM configuration, at least you’ll know what’s causing it. And you may then, working with your shop, be able to come up with a way to have your desired air intake mods and keep the engine working correctly too. Maybe you need some extra air baffling, etc. But you need to determine if that’s what’s causing the problem first.