I've had a CEL code 1131 for a few weeks now that I thought was related to the upstream o2 sensor. Well, I just got a call from my mechanic and the following was his diagnosis:

"There is no problem with your o2 sensors, the problem is your air intake system(just an 8" AFE, I haven't put on the SCA pipe yet). The open air filter that you have is changing the reading of the MAF and triggering a lean code. You need to put on your stock air box because that is what your MAF is calibrated for, otherwise you will end up damaging your car. I took off your filter and stuck my finger in front of the screen and moved it around which made the readings go from 1.7 to 8 (I don't really know what he is referring to?). "

Now, I will admit that I am not the most knowledgable car person, but I know that tons of people run aftermarket air intakes and I've never heard that they damage the car if installed properly. I suggested getting a different MAF that calibrated for my specific air flow requirements like the Proflow, and he didn't seem to be against that. So, basically, what I'm asking is for suggestions, ideas, info, etc.

find another mechanic...this sounds like he works on cars while holding a sandwich

The only reason I didn't write off his suggestion right off is that he IS a good mechanic that works on every kind of engine out there. He has a dual doctorate form MIT for god's sake. I don't know what's up, but I going to go pick up my car in a little while and try to get a better explaination.

I hear you. Same exact thing Ford told me about a month ago, about my after market intake. They said it was messing up the reading and if i didnt put it back to stock i would slowly damage the engine. So i have been driving with my CEL on for 2 months now because of this problem. I dont know what to do about it.

Anyone have an idea? Would putting an after market MAF on solve the problem? They qouted me a huge amount for them to "fix" this problem. They also told me that they didnt liked the mods i did to this car because it wasnt made to be modded . Anyways if you figure it out let me know..

Matt

Well, I went to pick up my car and got a better explaination. It turns out that what's causing the CEL is the flow of air into the MAF, specifically how the air is directed through the air filter. Apparently, there is a specific way that the stock air box directs the flow through the MAF. For example, when you take off the filter and idle the car and block certain sections of the MAF with your finger or other object, the car completely dies, but other sections are fine. These hot wire sensors are really picky about their readings . Anyway, I'm going to take myfastse's suggestion for now and rotate the MAF and see if the different positioning affects the reading. Other than that, I'm stumpped