Why does the Nissan Teana have unstable idle speed when cold?

[DeGabriela]

Reasons for unstable idle speed of Nissan Teana when cold: dirty throttle, slight lateral tilting of engine transmission, and ignition system failure. The following details the reasons: Dirty throttle: In cold conditions, carbon deposits will absorb part of the fuel, and if the fuel does not completely enter the cylinder for combustion, symptoms such as unstable idle speed and difficulty in starting will occur. Slight lateral tilting of engine transmission: Because there is a certain angle between the axial direction of the half shaft and the axial direction of the inner ball cage, the force point continuously changes back and forth along the axial direction during the rotation of the ball cage, causing vibration. Ignition system failure: For ignition system failure, it is necessary to check the spark plugs, cylinder wires, and ignition coils. Usually, leakage of cylinder wires or carbon deposits on spark plugs will cause vibration.

[AllieLee]

My Teana recently had the tachometer dancing during cold starts. This is usually related to carbon buildup, especially when the throttle body is dirty, which significantly affects air intake. When starting in the morning, the engine needs to maintain high RPMs to warm up. If the throttle edges are clogged with grime, the ECU can't properly control the air intake. Additionally, aging spark plugs have poor ignition efficiency in low temperatures, causing misfires and shaking. Another small detail is unstable fuel pump pressure or a clogged fuel filter affecting fuel delivery. When I fixed it, I first cleaned the throttle body, replaced all four spark plugs, and also cleaned the fuel tank. Now, cold starts are incredibly smooth every day—it feels like driving a whole new car.

[VonRebecca]

My neighbor, Brother Wang, who runs an auto repair shop, talked to me about this issue. A common cause for the Teana's problem lies in the intake piping. When the engine is cold, the rubber hoses harden, and cracks in the vacuum tubes can lead to air leaks. The ECU detects abnormal air intake and incorrectly adjusts the air-fuel mixture. Previously, my car had erratic idling accompanied by a coughing-like vibration. It turned out to be a crack in the hose connected to the air filter box. Later, I spent 180 to replace the entire set of rubber hoses and cleaned the air filter box thoroughly, which directly solved the problem that had been bothering me for three months. Remember, checking rubber components before winter is crucial.

[DeMalachi]

As a six-year Teana owner, I've found that unstable idle when the engine is cold depends on the situation. If accompanied by a pungent exhaust smell, it's usually due to an overly rich air-fuel mixture. During my last maintenance visit, the mechanic explained: The fuel injection volume is inherently higher during cold starts. If the coolant temperature sensor or intake air temperature sensor provides incorrect data, the ECU may inject excessive fuel, leading to incomplete combustion. I've personally seen an OBD scanner show short-term fuel trim values soaring to +25% during cold starts. A simple circuit test can confirm this – in my case, spending 300 yuan to replace the sensor fixed the issue. Regularly reading fault codes truly saves both hassle and money.