Idle Issues, things like slow idle, bad idle, lumpy idle, and fast idle — are symptoms that should be investigated, diagnosed and repaired.

Most Idle issues can be very frustrating, but with some patient troubleshooting, you’ll have a real chance at figuring it out.

Idle Issues
Idle Issues

Remember to always check your engine idle issues with the air conditioning and defroster turned off, as both of these systems are designed to change the idle when they are on due to the air conditioning system’s demands on the engine.


The engine will not properly idle, or will stall.  As a result, These symptoms may or may not be associated with one or more fault codes.


  • Throttle body is coated with carbon deposits
  • Maladjusted throttle stop
  • Vacuum leak(s)
  • Speed/Distance Sensor failure
  • MAP Sensor failure
  • Throttle Position Sensor failure
  • Automatic Idle Speed Motor failure

So, As you can see, there are many things that can be the cause of most Idle Issues.

Spark Plug

  • You may notice misfires, an increase in fuel consumption, loss of power and hard starting.

Air Filter

  • A clogged air filter may also cause an increase in fuel consumption, stalling, in extreme cases, and other driveability problems.

EGR Valve

  • An EGR stuck open may include a rough idle, rough performance at low engine speeds, stalling at idle, increase in fuel consumption, fuel odors, and possibly a check engine light on.

MAF Sensor

  • You may have power loss, surging at idle, hesitation, stalling during acceleration and other driveability problems.

ECT Sensor

  • With a bad ECT, you may notice a continuous lean or rich mixture, an increase in emissions and fuel consumption, and engine stalling when cold; operation may smooth out once engine temperature increases.

PCV Valve

  • Possible misfires, hard starts, and increase in oil consumption.

IAC Valve

  • You may notice a constant idle speed, either high or low.

Oxygen Sensor

  • A bad oxygen sensor will reflect primarily in the fuel injection system or the computerized carburetor system of your car, resulting in a rich or lean fuel mixture, increase in fuel consumption, or misfires.

TPS Sensor

  • A bad TPS may also cause stumbling, hesitation, surging, stalling and a hard starting.

Throttle Valve

  • Poor engine performance when cold or as it reaches operating temperature, hard starting, poor acceleration, rich fuel mixture at idle and stalling.

Fuel Pump

  • Noisy fuel pump, hard starting, power loss at highway speeds, engine stalling after a few minutes of operation.


  • A fault in one or more components in the system may cause the engine to idle poorly, stall, leak fuel and increase pressure inside the fuel tank.

Vacuum Leak

  • Besides a rough idle, a vacuum leak may produce backfiring, hard starting, stumbling, high idle, hesitation, misfiring, poor power brake action, and poor acceleration.

Head Gasket Leak

  • Missing, oil leakage, blue smoke, and overheating.

Choose Your Help Topic Below

Finding the cause of engine rough idle problems can be tricky at times. Paying attention to other symptoms besides the rough idle (shaking, noises, power loss) can help you close in on the source of the problem. And keep in mind that the most rough idles issues come from lack of proper maintenance.

So check those components or systems you have neglected lately. And scan your computer for possible trouble codes, even if the check engine light is not on. But, whatever the cause, don’t shrug off the problem, even if it seems to be a simple one, because it can result in a costly repair if you don’t take care of it now.