Your fuel system has the job of matching the amount of fuel to the amount of air your foot allows into the motor. The air mass meter gives a value for the air flow into the motor and is the most significant of the variables used in the fuel calculation.

Your system adapts using the feedback control (lambda cycle) to correct for mistakes it makes in the fuel calculation. The system is rather amazing as it has about a 30% ability to correct.

What happens is that a bad reading is interpreted and then a calculation is made. It is wrong and the system adapts to add the proper fuel. It does this adaptation at a particular load and then uses it in a multiplicative way to change the mixture in all settings. It then has the further capability to additively correct at idle one more time.

I see AMMs fail lean at load which causes a 1.15 and above multiplicative correction. This means it adds fuel (the limit is 1.32 on the adding side and .68 on the subtracting side). A characteristic of some failures is that they work all right at idle air flow. So because there is a 15% addition of fuel across the board it winds up 15% too rich at idle where it works correctly (an example - not all fail this way). At this point the idle is corrected with the CTP (closed throttle position) additive correction (up to 1ms). This is often what causes the code P0170 and P0173 for cars with a left side.

If you are having a running problem it is because the adaptations aren't working for you. If the adaptations are big and you reset them to zero you can then see how really poor the system would work with the parts as they exist.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician