Q: Car idle is erratic and exhaust gas smells strange.

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When I star the car, there's white smoke coming out of the exhaust and I think I noticed a bit of sweetness in its smell.My car idles really rough. Echos don't have RPM meter so I don't know how high but I'd say it's near 2000. Within the first 5 min after engine start, the idle starts to fluctuate continuously. Number-wise, I'd say it goes from 2000 down to under 500 and back up to 2000. It does so every 2 secondes and never stops doing so until I turn off the engine. Its winter right now in my area, so there ice pretty much everywhere. This problem makes taking off from stop pretty tricky because I can't keep a constant RPM under 4500. I'm basing all those RPM numbers on the noise. When manage to get the car going and switch to second gear, it accelerates on its own from 20 km/h to 35 km/h all while I never touch the gas pedal. All the way to 4th gear, it can keep a constant speed of 60 km/h while my foot sits way flat on the floor.

My car has 100000 miles.
My car has a manual transmission.

Hi There! It sounds like you may have a dirty or failing idle air control valve causing your engine idle to fluctuate and eventually stall. In the mornings it is normal for the engine idle to be a bit higher than normal when you start the car as this is the cold start enrichment process which allows the engine to warm up sufficiently, however this should cause the RPM’s to hover around 1,200-1,500 for a few minutes until the engine reaches operating temperature.

The idle air control valve is a small valve on the engine’s intake system that reads the air intake as it comes into the motor. This is controlled by the car’s ECM which uses this information to make adjustments to the air/fuel ratio depending on various inputs such as outside air temperature, intake air temperature, load and various other things. As you accelerate, your car’s engine is receiving a much higher dose of fuel than when at idle and conversely, when you let off the gas pedal, there is a sudden change in this fuel supply as a result of your foot letting off the pedal. When this happens, the job of the idle air control valve is to bring this deceleration down to a slow and smooth idle rather than suddenly cutting off the fuel supply causing the motor to die. The smell you are noticing may be a result of the inconsistent amounts of fuel being supplied to the motor as a result of the faulty idle air control valve. I would recommend having a professional come to your location to diagnose and inspect your vehicle.

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