986 Forum - The Community for Porsche Boxster & Cayman Owners - How to Test if MAF is working correctly

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Quote:

Originally Posted by mn box s

mentioned flickering of dome light etc. Same problem for me dont think its alt. or batt.
Have cel on with wandering idle my s has alittle over 60k Im going to replace all 4 02 sensors and my maf. If the problem persists Ill go from there.

Your posts are a ******************** to read...run on, incoherent, lack of punctuation, etc. This isn't IM. If people can understand what you are trying to say without needing a decoder you will receive some great info. Just a suggestion. :cheers:

Quote:

Originally Posted by xclusivecar

Hi,

Excellent point...

Happy Motoring!... Jim'99

Okay, I took it over to a porsche dealer and they ran a diagnostic and couldn't find anything creating the idle problem due a computer/cel issue. They were fairly sure that the idle problem was due to the throttle body. They wanted to replace the throttle body for $328 in addition to the $100 I had already spent for the 1 hour diagnostic. I opted to take it home and clean it myself. A quick trip to autozone, I purchased STP throttle body and air intake cleaner for about $3. After cleaning, the idle problem is NONEXISTENT!

The throttle body was extremely dirty, and to all of you with MAF problems due to not replacing the air filter regularly or due to an aftermarket oil type filter that was maybe over-oiled, you may also have the same exact problem as me if you have idle fluctuations.

Thanks for everyone's help in helping me diagnos my problem here. All is good now, but I'll be in touch when the next issue arrises.

Quote:

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.