Please explain coasting and idling terms applied to a vehicle.
I am not 100% sure; my understanding is that idling is a state of a drivetrain when the spinning engine is disengaged from the drive axle via the transmission: it's in Park or Neutral for an automatic transmission. That is, idling can happen (with foot off the gas pedal) both when the vehicle is parked or when the vehicle moves by inertia/gravity and is in Neutral.
Coasting, on the other hand, is a state of a drivetrain when the vehicle moves with foot off the gas and the transmission is in Drive, e.g., when going downhill or by inertia.
Also people say that you can save some gas when coasting but you always waste gas when idling. In other words, coasting is good, whereas idling is bad.
Idling is when the car is Turned on and is stationary be it in park or neutral.
Coasting is when you put the car in neutral when driving and inertia drive the car, be it on the flats or downhill, or even if the engine is cutoff and when the car is moving (eg. when the engine shuts off automatically on the highway, at that point the car is moving under it's inertia).
Apologies...I forgot to give you an upvote on this. Corrected now. {black}:cool:
Haha! Thanks @Mod_Man
Coasting is something the vehicle does. The engine is not longer accelerating the vehicle , but inertia is still carrying it forward.
Idling is an engine term. It means your foot is not on the accelerator pedal, and the throttle is open only just enough to keep the engine from dying. Typically around 700 or 800 RPM.
It is possible to be both coasting and idling at the same time.
Coasting vs Idling was already answered nicely by @WeAllBroke.
I just wanted to address the IAC valve question. @G.T. is correct: the IAC does play a part when a vehicle is coasting.
You can coast.
You can idle.
And you can coast and idle.
Coasting just means the car is moving by its own momentum. The engine can be on or off. If the engine is on, it is idling.
Idling means the engine is on, but is not being revived. The engine can be at idle in park or in neutral. The engine can be at idle while costing.
If a car is stopped at a red light and the transmission is in Drive (the driver is pressing the brakes to prevent the car from moving), is the engine idling? Thanks for your input.
I’d like to hear other opinions on this. This is my thought. It can go both ways.
On a very very very technical level, no the engine is not idling. Why? Because the engine is engaged to the transmission when at a stop light. So the engine is trying to make the car go, but the brakes stop it from moving.
But for most intents and purposes, it is idling, because the car isn’t moving, the revs are so low. And it is just waiting for more gas to rev up and go.
I would call that idling because you don't have any useful motion. ("idle hands"). If the engine turned any slower it would stall.
Me too.
Really appreciated, guys!
So the IAC (Idle Air Control) valve does its job only when the vehicle is stationary - be it in park on neutral?
Common sense tells me it should in coasting too
modern vehicles don't have an IAC valve. Idle air flow is controlled by the throttle.