i got a CEL a couple weeks ago and it was throwing a "manufacturer control fuel air metering" code. this made sense to me since i have been having some hesitation issues while under boost, like i wasnt getting enough fuel for the amount of boost. so i got a new mass air flow sensor and swapped it out. cleared the code and started driving it. everything was great. the CEL stayed off and the hesitation under boost went away also...the MAS seemed to fix all my problems. well things were good for about a week and then my CEL came back on yesterday, throwing the same code. what else could it be?? i looked and i cant find any vacuum leaks. i also had an old intercooler sitting around so i decided to change out whatever sensor that is that plugs into the top of the intercooler...figured that might be a down stream mas sensor of some sort. well i'm gonna give it a week or so and see if the CEL goes off on its own. but what else could be causing this???

 

You might wanna clear the code again after you change the sensor on the intercooler, I'm not sure that it'll just go away on its own. Besides that I'm not sure what would be causing it. If you have VAG COM I would suggest checking your multiplicative fuel trims:

http://wiki.ross-tech.com/index.php/Fuel_Trim_Info

Good luck!

 

The sensor you changed out is probably an IAT (intake air temp sensor). Do you have a boost gauge? What does it read? Check for a loose boost hose or clamp somewhere.

 

yeah i have a boost gauge and its reading good. i have always had a little bit low vacuu, reading (like 16 hg at idle instead of 20hg) but i have never thrown this code until recently so i dont think thats the problem. and i'm reaching full boost of about 17 psi and it sustains that, so i dont think its a boost leak either. any other suggestions?

 

Check fuel pressure or look for vacuum leaks. What do your pre-cat O2 sensor readings look like?

 

I have seen bad maf sensor out of the box. espically if you bought an aftermarket one. did you check the intake tube that goes from the maf to the turbo? Its made of cheap plastic it might have a crack in it.

 

^True. Or even debris gets stuck against the screen and can cause weird readings. What does the MAF read at idle with the a/c off? What about fuel trims?

 

i dont have vagcom or anything like that so i have no way of getting any of the readings that you are asking for. the maf that i bought is made by the same company as the old one that i took out so i'm assuming thats its been changed before, since i didnt get the part from the dealership. but i will take a look at the intake turbo inlet and see if their are any leaks there. are their any other sensors that play into this system? the fault code that it threw said that it could possibly be an O2 sensor as well, but the O2 sensors all throw their individual fault code as well so i figured that wasnt it. plus i'm still getting good gas mileage so i really dont think thats the problem. anything else?

 

Without readings from the O2 sensors, MAF, or fuel trims, you're kinda taking shots in the dark. Parts like that are kind of expensive just to throw in blindly. Try and get your hands on a VAGcom or make a friend with someone who has one.

 

The sensor on the ic is your map sensor. It's there so your ecu knows that the amount of boost that is requested is actual or very close. They arent known to fail. IAT sensor is on the throtle body.

Do you use an aftermarket intake or stock air box?