Engine
Rough Idle
Description
The engine shakes, vibrates, or runs unevenly when at a stop or in park. RPMs may fluctuate or drop below normal idle speed.
Common Causes
Worn spark plugs or ignition coils
Dirty throttle body or mass airflow sensor
Vacuum leak in intake system
Dirty or stuck fuel injectors
Low compression in one or more cylinders
Failing idle air control valve
Related Trouble Codes
P0100
Mass Air Flow Circuit Malfunction
Moderate
P0101
Mass Air Flow Circuit Range/Performance
Moderate
P0121
Throttle Position Sensor Range/Performance
Moderate
P0171
System Too Lean (Bank 1)
Moderate
P0172
System Too Rich (Bank 1)
Moderate
P0174
System Too Lean (Bank 2)
Moderate
P0175
System Too Rich (Bank 2)
Moderate
P0300
Random/Multiple Cylinder Misfire Detected
High
P0301
Cylinder 1 Misfire Detected
High
P0302
Cylinder 2 Misfire Detected
High
P0303
Cylinder 3 Misfire Detected
High
P0304
Cylinder 4 Misfire Detected
High
P0305
Cylinder 5 Misfire Detected
High
P0306
Cylinder 6 Misfire Detected
High
P0307
Cylinder 7 Misfire Detected
High
P0308
Cylinder 8 Misfire Detected
High
P0316
Misfire Detected on Startup (First 1000 Revolutions)
High
P0505
Idle Control System Malfunction
Moderate
P0506
Idle Control System RPM Lower Than Expected
Moderate
P0507
Idle Control System RPM Higher Than Expected
Moderate
P2187
System Too Lean at Idle (Bank 1)
Moderate
P2188
System Too Rich at Idle (Bank 1)
Moderate
Common Repairs
#1 Replace Spark Plugs
1–2 hours
$50 – $150
Easy
Worn or fouled spark plugs are the most common cause of rough idle and misfires on high-mileage vehicles.
Parts Needed
Spark Plugs (set of 8)
Ignition Coil Pack
#2 Clean Throttle Body
20–30 min
$5 – $15
Very Easy
Carbon buildup on the throttle plate disrupts airflow at idle. Cleaning often resolves rough idle without parts.
#3 Clean or Replace Mass Airflow Sensor
15–30 min
$8 – $120
Very Easy
A dirty MAF sensor sends inaccurate air readings, causing the ECU to run a rich or lean mixture causing rough idle.
Parts Needed
Mass Airflow Sensor
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Quick Info
| System | Engine |
| Related DTCs | 22 |
| Known Repairs | 3 |