Symptoms
- Engine dies at stop signs or in traffic
- RPM dips low before stalling
- Restarts fine afterward
- May be worse with AC or accessories on
Likely causes
- CommonDirty throttle body or idle air control valveCarbon buildup restricts the small airflow path needed to hold idle.
- CommonVacuum leakExtra unmetered air can push the idle mixture too lean to sustain combustion.
- PossibleFailing idle control or throttle position sensorBad sensor input confuses the computer's idle adjustments.
- PossibleDirty or failing mass airflow sensorInaccurate air readings can cause the fuel mixture to be wrong specifically at low airflow.
- Less commonLow fuel pressureA weakening fuel pump may barely keep up at idle and fail under the load of accessories.
What to do
- Get the check engine light scanned for idle, throttle, or fuel trim related codes.
- Check for obvious vacuum leaks: hissing sounds, cracked hoses, or a loose intake boot.
- Clean the throttle body with a throttle-body-safe cleaner if it looks dirty.
- Note whether stalling happens more with the AC or other accessories running, and mention this to a shop.
- Have the idle control valve or throttle position sensor tested if cleaning doesn't help.
- Have fuel pressure tested if electrical and vacuum causes are ruled out.
Tools and parts
- OBD-II code reader
- Throttle body cleaner
Throttle body cleanerSearch: “throttle body cleaner”
Idle air control valveSearch: “idle air control valve for [year make model]”
When to call a pro
See a shop soon, especially if stalling happens in traffic or intersections, since it's a safety issue as well as a mechanical one.
Safety
Use caution
Stalling in traffic can be dangerous; if it happens repeatedly, avoid busy roads until it's diagnosed and pull over safely if it happens while driving.