Foresyte27

I have literally replaced everything I could think of that is causing this rough idle, honestly I also think the tahoe is idling a little low in gear @500rpms... first to start, it is a 07 tahoe ls 4x4 with the AFM/DOD flex fuel 5.3 engine... I have pulled the heads because of a collapsed lifter on #1 (afm issue), replaced all gaskets topside, new plugs, wires, all 8 coil packs, mass air flow sensor, running 93 octane only in it, and it still has a rough and low idle in gear and at a stop... I don't know where to go from here, please help I've never had one I couldn't beat, but this 1 is really pushing it...

kevinkpk

What is the fuel pressure?

hanky

If the IAC (idle air control) is not functioning correctly possibly due to carbon blocking the passages,it restricts the amount of air going into the engine and the system responds with the correct amount of fuel in relation to the amount of air entering, it could be responsible for the idle problem.

Foresyte27

Fuel pressure is 55-60 and 07 tahoe with flex fuel doesn't have an IAC... at all... and the throttle body has been cleaned and reset...

kevinkpk

Back track, was this an issue other than the collapsed lifter before? This is a lack of fuel issue in my mind. Did the fuel pressure reading you had at the rail/injectors?

Foresyte27

Only issue was collapsed lifter on #1, fuel pressure is at the rail...

repairman54

Got AC plugs in it ? My '11 5.3 had a rougher idle with NGK plugs, back to AC and smoother.
Misfire counts on each cylinder will point out if it's only one or multiple cylinders .
Are your fuel trims relatively stable and in range? Both short and long term ones.

hanky

Usually , insufficient fuel pressure will affect high speed engine performance, but not idle.unless there is none or too low to run.
Did you ever run a compression check?
Most systems will adjust the injector on time based on the amount of air coming into the engine which the O2 sensors let the PCM know whether rich or lean.Do you have the equip to look at the fuel trim readings?

Foresyte27

Ac plugs, and fuel trim and o2 sensors good, replaced all o2 sensors...

kevinkpk

You said you replaced alot of things, how about the fuel pressure regulator? I read back through, and might have missed it, but didn't see that you checked it.