Here is some specifics:

04 Lariat Crew Cab
82k miles
5.4L
K&N 57 series intake


1. Truck ran fine, stopped at a store 10 min later truck barely started. I had to give it some gas to start.

2. Ran fine the next day then on my way home check light, popped codes P0174, P0171.

3. I cleaned the MAS with electronic cleaner cleaned my filter, and took the intake kit out to clean, which really wasnt dirty at all.

I tried to track down a new MAS but out of 6 local stores there were none in stock.

I have had the intake on for about a year and have not seen any issues from it until that day. Now I have a high pitched whistle noise when i hit 1500-2500 rpm, and will silence the instant I lay off the accelerator. I cannot recreate the noise when the truck is in park to locate the leak. Only sounds when driving?

What I'm asking is for possibly leak locations, locations of my o2 sensors and more than anything what you all think is the main reason for these sudden faults.

Oh just remembered that at idle my truck is usually about 550 rpm and now will dip to 400 noticeably shaking, but if i turn on the A/C the truck idles fine?

Thanks in advance for all your input.

 

Update**

I found that i can unplug the sensor to get the enginge to run in Failure Mode and Effects Management (FMEM). This apparently resets how the computer reads the information. I read that the computer gets accustomed to certain conditions and sets that as a "standard". I did this and my indicator panel stated Engine in Failure Safe Mode. I shut the car down, unplugged the negative, plugged the MAF back in and it was a dramatic increase in responsiveness and idling. But the truck will still stall after some time idling so im just going to replace it and see where that gets me.

Also is the whistling normal?