Today I took apart everything from the air filter up to the throttle butterfly valve. Checked and cleaned all connections, made sure everything was tight.

Started it back up and low and behold, the code didn't come back. Drove it around the block, still no code. Figured it was a loose connection or something and parked it. Took it out this afternoon, and the code did come back. However, my playing around with the intake obviously seems to have done something. Coincidental, or should I start replacing pieces of the intake and making sure everything is tight? The gasket in the throttle body seems like a good place to start.

 

Sometimes fault codes take multiple "drive cycles" for an error to be reported, or certain conditions must be met for the diagnostic monitor to run, so its very possible that the work you did, didn't change anything, but the test didn't run or didn't complete the first time you drove it.
Fault codes that set a check engine light on the first drive cycle are "Type A" fault codes and codes that require a failure on a second consecutive drive cycle are "Type B" fault codes.
OBDII - Diagnostic Trouble Codes - Types of DTC

 

Yeah I should have been more specific. The pending code didn't come back at first. It seems like a "Type B" fault code, it'll show up as pending until a second drive cycle when it triggers the CEL. However, after taking apart the intake piping, it didn't even show up as pending. Usually, as soon as I start it up, the code is there as pending, even if I clear it, it comes back immediately.

I'm going to start working to figure it out from both ends.

1. I'll swap the O2 sensors when I get a chance.
2. Going to start replacing pieces of the intake that might be suspect, starting with the gasket between the throttle body and intake and maybe a new air filter just in case.
3. Maybe replace the O2 sensors and/or MAF if I start getting desperate.

I know there are some seals deeper in the engine on the intake that I really don't want it to be. Could this have anything to do with EGR valve? No codes for that, but is it worth taking it off and trying to clean it out?

 

I'm thinking the code didn't come back immediately after taking apart the intake because the truck was started from cold, so was running open loop (no O2 input). When it warmed up enough to switch to closed loop, the code comes back.

Thinking this means an exhaust leak/O2 sensor are most likely culprit at this point.

 

Have you figured out what caused your code? I am getting same code and can't find anything on it