[Nitelife Mingus]

I’ve had a few situations my 2.0T (a8) will pulse a little but at cold startup/reversing out of my garage- almost as if I was lightly tapping my foot on the gas and revving the engine slightly. It goes away once the engine warms up. Has anyone else experienced this?

[ARCamaroGuy]

I have the v8 (2020) and mine does the same thing. It usually goes away after about 30 seconds or so but one time it lasted almost 10 minutes.

[crosive]

both my 2017 ss a8, and my 2018 zl1 a10 did this in cold enough weather.

lasted maybe a minute, not usually more

[gchu]

My 2017 SS Auto does the same - though I didn't notice it until after I installed a pray ported throttle body. Not sure if it was there before the install but it's definitely there now.... I usually just happens once (light a moderate tap of the gas). Happens whether I'm in gear (reverse or drive) or in park

Had thought about taking it into the dealer but figured they would just blame it on the ported TB.... Wasn't sure if a tune would fix it (all I have the GM CAI, Pray TB and a NPP with fuse pulled)

[ctrlz]

Depending on severity, this may be a problem with the idle air control (IAC) valve. This part is in charge or regulating airflow to maintain a smooth idle during cold start. The idle should start a little high, like 1300 rpm, and taper down over the first minute or so.

You need to see if the behavior is within parameters before bothering to change this out. Some of these are not that easy to remove from what I've read.

[m6-lt1]

Originally Posted by ctrlz

Depending on severity, this may be a problem with the idle air control (IAC) valve. This part is in charge or regulating airflow to maintain a smooth idle during cold start. The idle should start a little high, like 1300 rpm, and taper down over the first minute or so.

You need to see if the behavior is within parameters before bothering to change this out. Some of these are not that easy to remove from what I've read.

Just an FYI, 99% of cars sold in this day and age do not have iac valves anymore. Once cars switched to electronic throttle bodies, iac valves are essentially non-existent now as the idle is controlled by electronically.

[ctrlz]

Originally Posted by m6-lt1

Just an FYI, 99% of cars sold in this day and age do not have iac valves anymore. Once cars switched to electronic throttle bodies, iac valves are essentially non-existent now as the idle is controlled by electronically.

Yeahhh... I probably should've hit the repair manual first before speculating. Thanks.

On that note... the repair manual actually doesn't have that much to say about regulating idle for the 2.0 engine. It might be worth checking to see if the throttle body is firmly bolted down.

DESCRIPTION AND OPERATION > FUEL SYSTEM DESCRIPTION > STARTING MODE

The ECM supplies voltage to the chassis control module when the ECM detects that the ignition is ON.
The voltage from the ECM to the chassis control module remains active for 2 s, unless the engine is in
Crank or Run. While this voltage is being received, the chassis control module closes the ground switch
of the fuel tank fuel pump module and also supplies a varying voltage to the fuel tank fuel pump module in
order to maintain the desired fuel line pressure. The ECM calculates the air/fuel ratio based on inputs
from the engine coolant temperature (ECT), manifold absolute pressure (MAP), mass air flow (MAF), and
throttle position sensors. The system stays in starting mode until the engine speed reaches a
predetermined RPM.
During a cold start, the engine control module (ECM) commands dual-pulse mode during Open Loop
operation to improve cold start emissions. In dual-pulse mode, the injectors are energized twice during
each injection event.

DESCRIPTION AND OPERATION > FUEL SYSTEM DESCRIPTION > CLEAR FLOOD
MODE

If the engine floods, the engine can be cleared by pressing the accelerator pedal down to the floor and
then cranking the engine. When the throttle position sensor is at wide open throttle (WOT), the ECM
reduces the fuel injector pulse width in order to increase the air to fuel ratio. The ECM holds this injector
rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the
throttle is not held wide open, the ECM returns to the starting mode.

DESCRIPTION AND OPERATION > FUEL SYSTEM DESCRIPTION > RUN MODE

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and
the engine speed is above a predetermined RPM, the system begins Open Loop operation. The ECM
ignores the signal from the heated oxygen sensor (HO2S). The ECM calculates the air/fuel ratio based
on inputs from the engine coolant temperature (ECT), manifold absolute pressure (MAP), mass air flow
(MAF), and throttle position sensors. The system stays in Open Loop until meeting the following
conditions:
The HO2S has varying voltage output, showing that the HO2S is hot enough to operate properly.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.
Specific values for the above conditions exist for each different engine, and are stored in the electrically
erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after
reaching these values. In Closed Loop, the ECM calculates the air/fuel ratio, injector ON time, based
upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay

very close to 14.7:1.