2003 Suburban - Low Idle issues

[bladerunner77]

Ok, I'm at my wits end. Here are the details:

Bottom Line UP Front: I cannot resolve low idle issues -- 2003 Suburban 1500 KT Flex Fuel

I have done the following:
--> Replaced Air Filter
--> Replaced the MAF Sensor
--> Replaced all plugs and wires
--> Replaced Fuel Pressure Regulator
--> Replaced Throttle Body Intake [TBI] (a.k.a Air Intake Manifold) - TPS is included in unit
--> Replaced TBI gasket***
--> Cleaned as much of the air intake system as I could

*** I replaced the TBI gasket after getting engine code P0171 and P0174 - System Too Lean (bank 1 and bank 2, respectively). I have cleared the code and it does not come back up; however, I still have idle issues.

My symptoms:
- After initial start, approximately one minute (or less) the engine begins to idle low, rough and sporadic - but not to the point of stalling. Driving for approximately 5 - 10 minutes to warm engine to 180+ degrees, the idle roughness is significantly lessoned at stops. When in park, after driving and truck at operating temp, it takes about 30 sec to a minute when some rough idling occurs.

I do not get any codes that indicate cylinders misfiring but I do not know if this could be an injector circuit malfunctioning or some or related issue.

Any thoughts or insight would be GREATLY appreciated!

[Pikey]

How does it drive other than the idle? Clogged cats? if it has an egr valve I would pull it off and clean it also.

[bladerunner77]

How does it drive other than the idle? Clogged cats? if it has an egr valve I would pull it off and clean it also.

Once i'ts reached normal operating temps, the idle levels off. However, if I sit at a liight for a while it will get sporadically rough. Outside of that, normal driving is fine with no issues.

This is the first mention of the EGR valve having an effect.. I'll check it. What about the EVAP - can it effect the idle.. does the this model have an IAC?

[Pikey]

I think that my 03 did not have the iac. But, I am not sure. If it has an EGR (my 02 did not) you can clean it with brake clean and get a new gasket for around $4. It is a long shot, but I have seen stranger things cause a bad idle.

[bladerunner77]

I think that my 03 did not have the iac. But, I am not sure. If it has an EGR (my 02 did not) you can clean it with brake clean and get a new gasket for around $4. It is a long shot, but I have seen stranger things cause a bad idle.

I did a lot more digging and found out the following:
--> I do not have an IAC or EGR valve on this model year
--> I continue to pull codes P0174 and P0171 (system too lean banks 2 and 1, respectively)

--> The rough idle continued even after replacing the TBI gasket and cleaning the intake system, so with some other suggestions, I added SeaFoam to the tank --- it significantly improved the rough idle -- it's only marginally noticeable at ldle and in park (cleaned the fuel injectors well).

However, the idle is still low and I continue to get the codes once cleared. Based on other research and suggestions, I think I have a couple more things I can do:
1. Replace the O2 sensors - pre and post cat converter
2. Replace Manifold gaskets

Any thoughts or other suggestions? Thanks!