Where the Highlander's −46% came from

November 6. What was seen with the dirty MAF sensor

The oil and air filter had not yet been changed. Between two measurement series with the dirty sensor, normalized airflow rose from 7,76 to 12,12 g/s per 1000 rpm. In the second series, the engine control unit reduced fuel delivery on both cylinder banks. The combined short-term and long-term trims were −31,6 and −27,2 percentage points, and λ dropped to 0,9663. This λ value indicates enrichment in this record.

The car did not yet have its own baseline for comparison in this mode. The AI0.19 rule was able to flag the anomaly without one. In the historical replay at 17:08 Omsk time, it generated a warning about high MAF readings at warm idle with enrichment. The combination of readings pointed the inspection toward the sensor, its connector, and the air duct.

That same day, the dirty MAF sensor was replaced with a new one, keeping the old filter. In later records at idle, normalized airflow returned to roughly 6–7 g/s per 1000 rpm. One early pair of measurements looked like a recovery, but on inspection the load turned out to be different. So the replay excluded it from confirmed recoveries.

November 7. What the filter replacement showed

First the oil was changed, then the air filter. According to the owner, the car covered 16 681 km on the previous oil. After the oil change, the idle fluctuated slightly. After the filter, in the driver's perception, the engine ran more smoothly.

RPM. In the historical replay, the average RPM variation within short segments decreased from 11,67 to 4,42 rpm, roughly by 62%. Three segments before the replacement and six after were included. This is a preliminary result consistent with the driver's impression. It can be verified with another one or two ordinary drives.

Air and mixture. There were not enough joint measurements for a full assessment under the app's rules. In this sample, for airflow there were 0 measurements before and 1 after, and for fuel trims — one each. We separately looked at airflow across the available records at comparable warm idle. The averages came out to 3,55 and 3,53 g/s before and after the filter. In other words, RPM within short segments became steadier, while there was no notable increase in airflow at comparable idle.

Why −46% was shown on the screen

LLCAR compared 5,04 with 9,39 g/s per 1000 rpm in the 0–20 km/h speed range. The second number came from the car's stored history. The 46% decrease was calculated against this baseline. In the filter measurement, we compared two segments of the same evening with the new sensor already installed.

After the service, one more question remained. The lean-mixture codes P0171 and P0174 appear in stored records as early as October 27, and then again on November 9–10. These lists preserve the code history. Assessing the current state requires a new scan and fresh measurements while driving.

How to repeat the check

1. With the engine warmed up, record 5 minutes of idle in an open area. Apply the parking brake and leave the transmission in P.
2. Drive 15–20 minutes on a familiar route at your usual pace. Return to the same area and record another 5 minutes of idle. Review the readings after stopping.
3. Repeat the loop twice more with the same fuel, load, and air-conditioning settings. Mount the phone in the same position. Save RPM, temperature, airflow, both fuel trims for every available bank, and codes. Do not reset codes or adaptations between runs.

For comparison with this service, look for baseline measurements taken after the new MAF sensor was installed but before the oil change. That gives you a chance to compare similar conditions and see whether the result holds from trip to trip. If the engine shakes severely or the Check Engine light is flashing, stop in a safe place and seek assistance.

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