Uneven Airflow Readings Have This Driver Stumped - Here’s What Might Be Going On

A driver recently brought in a head-scratcher: the car runs fine, but the data tells a different story. At idle, the mass airflow sensor on bank 1 reads just 2 grams per second, while bank 2 shows 7 grams per second. Meanwhile, long-term fuel trims are off balance too, bank 1 sits at -10%, and bank 2 at +1%.

That kind of disparity usually points to something mechanical or a sensor issue, but the usual fixes haven’t solved it.

The owner had the fuel injectors replaced about 10,000 miles ago, and the MAF sensor has been thoroughly cleaned and swapped between banks to rule out a bad sensor. Despite those efforts, the readings remain stubbornly unbalanced. With the engine running smoothly, it’s tempting to ignore the numbers, but such a wide gap in air measurement often leads to drivability problems or emissions failures down the road.

So what could cause this? A vacuum leak on bank 1 might trick the MAF into reading low, while a restricted intake or exhaust on bank 2 could push its reading high. Another possibility: a failing PCV valve or a dirty throttle body that’s affecting one side of the intake more than the other.

The fact that the long-term fuel trim on bank 1 is negative (-10%) suggests the computer is pulling fuel, meaning it thinks that bank is running rich, possibly due to unmetered air. A smoke test for intake leaks and a close look at the intake manifold gaskets would be a smart next step.