Home made cold air intake could be the problem.

 

Yeh I agree. Do you still have the stock intake to put back on? Also did you install the cat-back yourself? You may want to make sure all of the flanges are nice and tight.

As for your homemade intake, do you mind taking a picture of it? Also there are a few sensors that come off that intake tube. Were the original ones pluged in? Because if they are not getting a reading, then that is going to cause your truck to run like ****.

Sounds like everything else is in good condition.

 

I just had this kind of thing happen recently, the vac hose that goes from under the throttle body to the evap. canister thermistor got dry rotted came apart. It was causing lean codes on either, and both banks, a random multiple misfire code, and idled horrible, would almost stall, then surge at high idle, but would run pretty smooth going down the road. Put a new vac hose in the bad ones place, cleared the codes and all is well again. Almost any kind of leak from the air filter/maf sensor to the motor WILL cause lean codes, usually on both banks, but mine would show codes for 1 or 2, and codes for both.

 

have you thought about doing a full tune-up to the engine? if you have random miss fire it could be caused by bad wires,plugs a fuel injector not firing right, vac leak, um couple other things but i just woke up. so i will think about them and post later

 

I will check out that vac line going to the evap canister.... i don't see how the intake would be the problem, but I will check it for leaks?... And yes, all the sensors were plugged in... Give me a little credit here... And the exhaust is fine, no leaks, and the flange is tight... i will maybe test the wires for resistance and see if they have degraded to the point that they should be replaced... Thanks for the input...

 

So I was driving to work yesterday, and the CEL came on again... This time it was 171 & 174 - System too lean both banks... Help.. before I burn it....J/K

 

The only thing that makes sense is a vacume leak. My guess is lower intake manifold gaskets. You can try spraying some brake-clean around the gasket areas of your intake manifold while the motor is running. If you hear a change in the idle then you have found your leak.

I had the same issue on mine and my roomates 97 rangers with the 4.0

 

Fords are know for p0171 and p0174. Most of the time it is due to Unaccounted for air, or most commonly know as a vacuum leak. A vacuum leak is much more common that MAF issue. I highly recommend replacing intake manifold gaskets since you have already verified all other external vaccum leaks have been sealed.