iBoell

still trying to figure out an issue i may be having with the afm. wondering if a cold motor ignores the afm.

MudHippy

The voltage signal from the AFM is never ignored. Especially not in open loop(when the O2 sensor signal isn't also being used to make minor corrections). The easy way to think of it is...the engine(or rather the engine's ECU) ALWAYS needs to know the volume of air flowing into it.

http://www.autoshop101.com/forms/h44.pdf

iBoell

okay thank you. im trying to diagnose this hesitation problem that only occurs once the motor is warmed up. i guess that rules out the afm... dangit.

BamaYota1

Check your O2. It is the primary sensor used in closed loop, which is what you are in when the engine is warm. Is it hesitating under partial throttle? Is it hesitating under wot? Wot ignores O2, partial throttle doesn't.

iBoell

DENSO O2 sensor just replaced as part of the check list. problem remains. it is only under partial throttle.. cruising speed. can also memic issue in neutral under a steady hold.

BamaYota1

Cruising speed at partial throttle should be closed loop. Have you checked the afm per the FSM? TPS?

Gamefreakgc

The most common temperature related sensors that cause issues (works well cold, issues when warm) are the Engine Coolant Temperature sensor (ECT), VAFM, Throttle position Sensor (TPS) and O2 sensors. Start there, chances are one of those are your issues. Not that only the O2 throws a code when it's bad, the rest will silently degrade your engine performance.

I had a bad TPS and ECT when I got the truck and didn't know until I just decide to blindly test them one day. After replacing/tuning both it's like I have a brand new truck.