2009 Tahoe Rough Idle RPM Fluctuation

[winmag45]

I know others on this forum have had this issue and Ive tried some of the suggested remedies.I think I am getting close but the check engine light keeps coming on at start up in the morning.The RPM fluctuates 500 to 400 and back then settles,then it starts again.Changed the MAS,fuel pump,all filters,plugs,wires,cleaned the throttle componets,etc,etc.The error codes have been P0174 and P1400.I was wondering if a retune would help?Any other suggestions are greatly appreciated.Thank You

 

[sumo]

Check your intake tube? Sound like you have some unmetered air like a leak and the pcm is trying to compensate for it but doesn't know how

 

[NGAneer]

Agreed. System lean is likely before the intake manifold. Check TB seal, intake piping, etc. Maybe a constant vacuum leak, check under the engine cover. Definitely sounds like you've got come unmetered air. I like using brake cleaner, WD-40, etc. to check for leaks. Any little leak will suck that stuff in and the motor will react and you've found your leak.