Stalling at Cold Idle - 2002 Chevy Silverado 1500 (5.3L - 4WD)
I have a 2002 Chevy Silverado 1500 (Vortec 5.3L V8 - 4WD) with 215k miles
that doesn't want to run when cold. On a cold start, it normally idles up to
1000 rpm and slowly drops down. Currently, it gets up to 1000, falls to 500,
then comes back up and dances around 700 before dropping down. Not
ideal, but not a problem either...until you drop it into drive. If you put it in gear
and try to set off, it stalls when you let your foot off the throttle. Acceleration
is fine when cold, it only wants to die when it needs to idle (at a stop or going
around a corner - bogs down to 20 rpm and dies sometimes). KEEP IN
MIND THAT ALL PROBLEMS GO AWAY WHEN WARM.
No Check Engine or ABS light, ran it for codes anyway:
P0102 - MAF Sensor Circuit Low Frequency
C0225 - Front Left Wheel Speed Sensor Short Circuit or Circuit Open
C0227 - Front Left Wheel Speed Sensor Circuit Open or Short
C0226 - Front Left Wheel Speed Signal Missing
My thinking was that in open loop operation (running purely on MAP and
MAF sensors when cold), it had to be an issue with MAP or MAF sensor.
Cleaned throttle body, cleaned MAP and MAF, replaced air filter,
disconnected the battery and drained the ECU for a reset, hooked it back up,
no change.
I ignored the speed sensor and chased MAF problems. Low Frequency is
caused by either not enough air flow through the MAF or bad ground.
Replaced the MAF, problem persisted, returned it and put the old one back
in. At the electrical clip for the MAF I have good voltage on the power and
signal wires, as well as solid grounds and good reading on the IAT (built-in to
the MAF and runs to the PCM). Crawled underneath the frame and around
the engine bay and cleaned all my grounds with a wire brush and wire wheel
on my grinder. Reattached all my wires, no change.
Chased vacuum leaks for a while. Sprayed down the entire engine bay with
starting fluid and propane both. Couldn't find anything, and I can't hear it
sucking air anywhere. I had replaced my intake gaskets last year so I re-
torqued the bolts just in case. No change.
I figured since my grounds are good and no vacuum leaks, it must not be
sucking enough air bc it's trying to balance out low fuel consumption. I had
previously replaced my Idle Air Control Valve last year and it was working
fine so I started diagnosing the fuel system. I replaced my fuel pump and
filter last year along with the IACV; that only left EGR, fuel pressure
regulator, and the injectors. Cleaned EGR (no significant carbon depsoits). I
have fuel pressure in spec (on the low side - just 1 psi inside the range) and
it will hold steady pressure like it should. Pressure regulator was working fine
(noticed an 8 psi difference in pressure when removing the vacuum hose).
That left fuel injectors. I pulled them today and I'm going to run carb cleaner
through them and replace the O-Rings in case they're leaking or dirty. Don't
suspect leakage bc no fuel smell in engine bay and it isn't running rich or
anything. Don't really think they're dirty bc they don't look bad (I run injector
cleaner through my gas at every oil change) and I'm not getting misfires or
knocks. Will put them back in tomorrow and see what happens.
In the meantime, does anyone have ideas? I'm chasing ghosts at this point.
The only other ideas I have is that somehow the faulty speed sensor is
messing with the PCM or there's something screwy with the Throttle Position
Sensor (but I have an actual throttle cable so my butterfly is fully closed and
it's all on the IACV at idle so I don't think that's the case). I really don't know.
Maintenance already performed:
New Battery and Alternator a year and a half ago
New Spark Plugs and Spark Plug Wires a year and a half ago
ECT Sensor replacement and coolant flush 2 years ago
Please help! I'm out of ideas and without a live scan tool I'm just fumbling
around in the dark here.
