Fast Idles on Start-up

[StevieC]

Does anyone know why Toyota and some other OE's have fast idles on start-up and then drop to a normal idle after a period of time?
Like someone just hits a switch at the 30 second time limit and then it drops right off.

I'm assuming this is to circulate the oil and warm up the Catalytic / AFR's and 02's. My Highlander will run about 1,000 rpm on start-up I've noticed if the engine is below 100F water temperature and stay there for about 30 seconds before dropping off to normal idle. It also does this same period of time if it's bone cold from sitting overnight for example.

With my previous vehicles (Journey, Santa Fe, Ford Tempo) they would only idle faster in extremely cold weather only and then would slowly drop to 650 rpm sort of thing as the vehicle warmed up.

Just curious if anyone knows the official reason behind this setup versus the other.

 

[Eddie]

My Mazda starts up at ~ 1,500 rpm and drops to 800 or so after 30 seconds depending on the temperature. The high idle speed heats up the catalytic converter quickly to reduce engine emissions. Ed

 

[NHGUY]

Cold engines stumble with an instant low idle.Add an instant high idle,build a slight amount of heat and fuel flow and then you can back it down.Also helps charge the battery after the cranking.

 

[Warstud]

Could be the smog pump

 

[clinebarger]

It's to Light the Catalyst, Manufactures have used this strategy for a while now. It may vary depending on how close the converters are to the engine. Just about everyone has used "Close Couple" for the last 10 years.

 

[clinebarger]

Originally Posted by Warstud
Could be the smog pump


Most gas engines have evolved past using a A.I.R/Smog pump along with the EGR.

 

[StevieC]

We haven't had Smog Pump's here since the 1970's.

 

[StevieC]

Originally Posted by clinebarger
It's to Light the Catalyst, Manufactures have used this strategy for a while now. It may vary depending on how close the converters are to the engine. Just about everyone has used "Close Couple" for the last 10 years.


If mine were any closer they would be incorporated into the heads.

 

[Trav]

Originally Posted by StevieC
We haven't had Smog Pump's here since the 1970's.

Sure you have they are called Secondary Air Injection Pumps. Belt driven pumps went away in the 80s IIRC.

 

[StevieC]

I have spent most of my time working on Asian and American vehicles and haven't come across any. I have seen Air Injection pumps on German vehicles but we don't refer to them as Smog Pumps. Smog pumps or so they were called were compressor looking things that were belt driven and forced air into the catalytic converters and that type I haven't seen since the 1970's vehicles. Gasoline based anyway.

 

[clinebarger]

Originally Posted by StevieC
Originally Posted by clinebarger
It's to Light the Catalyst, Manufactures have used this strategy for a while now. It may vary depending on how close the converters are to the engine. Just about everyone has used "Close Couple" for the last 10 years.


If mine were any closer they would be incorporated into the heads.

You also have to account for only 3 cylinders lighting off a single catalyst, Where 4 cylinders would probably light it faster.

*Tightening emissions regulations, I would suspect/expect your 2018 has to meet tougher standards than your older vehicles.

 

[StevieC]

It's also a ULEV-II emission rated vehicle as well so I'm sure that also adds to the burden of warming up the Catalyst as well.

 

[Trav]

Pull back the L/side front bumper of many GM cars and you will find your electrically driven smog pump.

 

[hpb]

1000 rpm is a pretty low "fast idle", modern Subaru's sit just under 2000 rpm for the first 10 seconds or so. As others have said though, it's designed to light the cat off as quickly as possible.

 

[StevieC]

It might be faster once the cold weather arrives but right now with it being in the high 70's and mid 80's it's 1,000 rpm on start up.

 

[OVERKILL]

Originally Posted by Trav
Originally Posted by StevieC
We haven't had Smog Pump's here since the 1970's.

Sure you have they are called Secondary Air Injection Pumps. Belt driven pumps went away in the 80s IIRC.


90's on the Ford Windsors.

 

[FCD]

My 1988 Escort, with Bosch K-Jetronic Mechanical injection does fast idle for about 5-10 seconds at 1100 rpm, despite having no cat or any other emissions eqiupment from the factory.
Gotta love K-Jet, beautifully over-engineered ( although reliable )

 

[demarpaint]

Originally Posted by StevieC
It might be faster once the cold weather arrives but right now with it being in the high 70's and mid 80's it's 1,000 rpm on start up.


I'm sure it will idle faster when it gets colder. As of today every car I ever started had a faster idle than normal for a few seconds to a few minutes depending in the ambient temperature. MFG's want that CC hot fast.

 

[SteveSRT8]

According to an actual GM engineer who collaborates with our authorized upfitter it is for lubrication. Our 6.0 fleet vans rev to 1300-1400 immediately on startup. A bit disconcerting until you get used to it...

 

[billt460]

Every car I've ever owned or driven in the past 55 years fast idles on a cold start. The colder the longer it does so. Carburetors had automatic chokes along with fast idle cams you set by depressing the accelerator once to the floor. Fuel injected engines do it though the computer. You simply turn the key with your foot off the pedal. With the chokes and cams you had to, "kick them down" by stabbing the accelerator after they ran for a couple of minutes. Today's cars reduce RPM automatically as the engine warms up.