baege

So something I've noticed is a rather peculiar idle trait on the 4.0 compared to the 3.4's I've had before.

on a pure cold start the usual high idle at about 1100 rpm continues for about 20 seconds or so and then it drops to a normal idle speed

but I have noticed that on semi-cold starts, after I've driven it for a while and then it sat for a couple hours or so but is still warmer than a cold start, it will also do the fast 1100 rpm idle upon start up but it will stay at that speed for a noticeably longer period than at a pure cold start

anyone else experience this?

dichael

Idk if this helps… I’ve def noticed the pure cold start scenario, but haven’t noticed the semi cold start scenario where it stays at high rpm’s longer.

smegman

I wouldn't worry about it, its just computers doing computer stuff

c1pher

If my car is still warm, it doesn't go to high RPM like it does when first started in the morning.

clutchplate

Mine's the same.

Bents

Definitely a choppy idle. Adds to the character.

baege

my idle twin!

does it concern you at all?

I just think it's odd and annoying to wait that long until it actually goes back to normal idle speed

with a pure cold start it's only about 20 seconds, but with the semi-warm it can idle high for more than a minute before it drops down..

clutchplate

I never noticed it until I saw your post. Started it this morning after it was warm and it stayed at 1,100 for around 30 seconds, maybe a little more. Probably normal.

Reedy

Even when the engine is warm the CATs still need to be heated to operating temperature.

ttcbj

Yes, I believe this is for emissions, and is related to warming up the Cats.

patdonahue

Same here, I can drive it 40 miles shut down for 30-40 minutes to get a burger and on restart it will pop up to a slightly high idle. I think Reedy & ttcbj have the answer.

JAhmed

Yup

baege

thanks for the responses that provide a reassuring explanation, this community rocks
so the next question is of course do I need to wait everytime for the idle to drop to normal speed before driving off when starting after semi-warm?

Reedy

No it's not necessary, especially when its already warm. Even when dead cold it isn't necessary as long as you aren't redlining it straight away.

YTownSpyder

It’s 100% heating the cats. I’ve heard multiple automotive engineers explain it. Pod cast but none the less an explanation