thoughts on these trouble codes?

[matt351]

Hi guys. My truck is running fine, just getting poor fuel mikeage (13mpg'ish). I went by Autozone and had them run the codes.

P0174 - fuel trim, bank two
P0171 - fuel trim, bank one
P1506 - IAC overspeed error
P0457 - EVAP small leak detected

I have a feeling I know what the P0457 is... I capped off the vac fittings on the underside of the upper intake. I believe they were some sort of vent from the fuel tank. ThE IAC code kinda threw me because I cleaned it out reaply well a couple of months ago. Maybe it just needs replaced? Also, are the first two codes saying I just need o2 sensors? With almost 200k on this thing I'm not suprised that they'd need replaced lol.

 

[koda2000]

all the codes are related. you have a vacuum leak (besides the leak in the evap system). if you have the SOHC V6 you probably need to replace at least the upper intake manifold O-rings. also check the PCV elbow and other vacuum lines/connections. your IAC is probably fine, the PCM just can't adjust it to compensate for the unmonitored air getting into the intake.

At 200K you're due for upstream O2 sensors, but that's not related to the codes you're getting. they can effect your fuel economy adversely though.

 

[matt351]

Okay great thanks! Yeah I do have the sohc motor. I pulled the upper last fall and I had a heck of a time getting this plastic tube that runs into the upper intake by the IAC from the air intake just aft if the MAF sensor to fit back on there. I ended up hose clamping it down as best I could, but I have a feeling that could be my culprit.