Friday February 16 2018

Do I need to idle my engine in the morning?


Hi Paul, I enjoy reading your car articles. My question is, should I idle up my Toyota Harrier engine for some time when I start it every morning as a way to improve a recent engine hesitation? When I was growing up, my father used to do it to his Peugeot to allow the engine stabilise in the morning. Musoke.

Hello, Musoke, you do not need to excessively idle your engine to stabilise it during cold morning starts.
Your car engine management system may be faulty. Internal combustion engines such as the one on your car generally run smoother and more efficiently when they warm up and use hot engine blow by gases and coolant to pre-warm the intake air fuel mixture for more prompt and efficient ignition.

When the engine is cold it does not burn fuel efficiently and may hesitate when you try to accelerate.
On the old, classic cars such as your father’s Peugeot, the engine carburetor (air intake system) is mechanical and so is the process of adjusting the fuel air ratio to speed up warm up phase and stabilize engine runnning.

A driver of the early generation engines has to manually pull a lever to adjust a plate in the carburetor, for a short time, to choke the engine and regulate the fuel air mixture during cold starts.
Choking runs the engine richer to allow it warm up faster and stabilise. Newer generation engines with electronic fuel injection have an engine management system (engine computer).

This system relies on sensors which monitor intake air temperature, coolant temperature and exhaust temperature to automatically adjust the fuel air ratio which increases engine revs for a short while in order to stabilise the engine during cold start running.

When you start your car engine you can drive away because the ECM will automatically adjust and adapt engine tuning to the cold running condition.
When the engine management system sensors which monitor the coolant temperature and intake air temperature sensor fail, you are likely to experience difficult cold starts.