[blue2000s]

Originally Posted by MNBoxster

Hi,

Sorry, the car does not rely on MAF readings when the engine is cold. It takes only approx. 10-15 sec. for the O² Sensors to come up to operating temperature, they are heated sensors with an induction coil or heater to do this. Until then, the DME operates in what is termed an Open Loop, meaning that it isn't sampling anything, just operating on a default MAP.

The MAF Sensor and O² Sensors work in conjunction with the DME in Closed Loop operation where the Air Mass measured (along with other variables like Engine Temp, Load, Speed, Fuel Quality, etc.) determines which Fuel/Timing MAP is selected.

The Pre-Cat or Primary O² Sensors verify or corroborate this selection with post combustion Oxygen Sampling, which is further refined by the Post-Cat, or secondary, O² sensors sampling the same exhaust pulse to determine the Cats efficiency in managing the Emissions requirements.

One of the reasons (but not the only one) why an engine with a failed MAF will exhibit popping is that the DME gets an unrecognizable signal (including no signal) from the MAF. If the MAF has failed, the signal is interpreted as too much Intake Air and the DME enriches the mixture, which then does not fully combust inside the combustion chamber and passes through to the hot exhaust where it spontaneously combusts causing the Pops. On primarily a dirty MAF, the dirt/oil acts as insulation not allowing the Intake Air to extract any heat from the Hot Film. The resistance or voltage (depending upon type) doesn't change which the DME interprets as a lesser Air Mass. Consequently, it leans out the Fuel Mixture, often resulting in poor starting, low performance, hesitancy. Just FYI...

Happy Motoring!... Jim'99

The ECU will use the MAF when the engine is cold to determine load conditions. The MAF is used with and without inputs from the O2 sensors.

In fact, even when the car's hot, it will go into open loop mode during transient conditions because of the lag in O2 sensor feedback. The load data comes from throttle position and the MAF.