Rough Engine Idle
A rough idle usually comes from a misfire, a vacuum leak, dirty injectors or a dirty throttle body.
Can I drive it? Drive with care
Usually fine to drive gently. A flashing check engine light means stop and get it checked.
Typical repair cost
$5-$20 for cleaner, $100-$300 for plugs or coils, $150-$400 for a vacuum leak, $100-$250 for injector cleaning.
General US estimates, not quotes. Prices vary by region, vehicle and shop.
Symptoms to Look For
These signs indicate you might be experiencing this issue
- Engine shakes or vibrates at stop lights
- RPM needle fluctuates at idle
- Car feels like it might stall when stationary
- Excessive vibration through steering wheel
- Poor fuel economy in city driving
Potential Causes
Most likely reasons for this problem, sorted by probability
Repair Solutions
Step-by-step instructions to diagnose and fix the problem
1Clean Throttle Body
- 1
Disconnect battery negative terminal
- 2
Remove air intake tube to access throttle body
- 3
Spray throttle body cleaner on cloth (not directly)
- 4
Clean carbon buildup from throttle plate and bore
- 5
Reinstall components and reset ECU by disconnecting battery
Need professional help?
Find a repair shop near you, or describe your exact symptoms to the AI mechanic
When to See a Mechanic
Do not wait if any of these apply
- The check engine light is flashing
- The engine stumbles or stalls when warm
- The roughness started right after a repair
How to Prevent It
Simple habits that stop this problem coming back
- Replace spark plugs at the interval in your manual
- Use Top Tier fuel
- Have a carbon-coated throttle body cleaned using the vehicle's procedure
Frequently Asked Questions
Why does my car idle rough only when cold?
Cold-only roughness often points at the coolant temperature sensor, vacuum leaks that seal as parts expand, or carbon deposits. Note when it clears; that helps the diagnosis.
Can a weak battery cause a rough idle?
Yes. A weak battery or failing alternator makes the computer compensate, which can cause a hunting or uneven idle.
Related Trouble Codes
Codes a scan tool may show with this problem
Related Issues
AI-generated and informational only. This is not a diagnosis of your specific vehicle and does not replace inspection by a qualified technician.