Rough Idle

What it feels like

• The steering wheel or seat vibrates while you sit at a light
• The tach needle drifts up and down a little on its own
• The exhaust note pulses instead of holding steady
• It clears up as soon as you touch the throttle

Codes that usually produce this

• P0300 Random or Multiple Cylinder Misfire Detected Stop driving 2 weeks estimate
• P0301 Cylinder 1 Misfire Detected Stop driving 2 weeks estimate
• P0171 System Too Lean (Bank 1) Drive with caution 2 months estimate
• P0172 System Too Rich (Bank 1) Drive with caution 1 month estimate
• P0101 Mass Air Flow Sensor Range / Performance Drive with caution 6 months estimate

Check these first, in this order

Free checks first. Nothing here costs money except the fuel you burn.

1. 1

   Open the hood with the engine idling and listen along the intake tube from the air box to the throttle body.

   What you'll seeA steady hiss. A whistle that changes when you wiggle a joint is a leak.

2. 2

   Pull the mass air flow sensor out of the intake tube and look at the wire element inside.

   What you'll seeA clean bright wire. Any oily film is enough to rough up the idle.

3. 3

   Watch the misfire counters at idle for two full minutes without touching the throttle.

   What you'll seeEvery counter at zero. One that climbs points at that cylinder.