Fast Idle at cold start

Mikebuild

Original poster
Member
Mar 16, 2012
4
Hey, need some help ...

'04 TB 4.2; auto; 4wd; 118k miles

At cold start up it will idle at ~1500 rpm and gradually settle down to normal (~7-8 seconds).
Does this everytime. Whether codes present or not. Have had no codes for quite awhile.
Recently had code P0128 and P0410. Have fixed P0128 (new tstat and sensor) and am working on P0410 (am attempting to verify solenoid function/pump works).

This condition persists regardless of codes.

Where to begin?
 

Wahugg

Member
Dec 4, 2011
87
This is completely normal. All the engine is doing is idling higher to help reach its operating temp faster. So don't sweat it, it's perfectly normal.

-Wahugg
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
This table is built into the PCM programming, unless it's been fiddled with in a tune:

idle.jpg
 

CaptainXL

Member
Dec 4, 2011
2,445
Mikebuild said:
Hey, need some help ...

'04 TB 4.2; auto; 4wd; 118k miles

At cold start up it will idle at ~1500 rpm and gradually settle down to normal (~7-8 seconds).
Does this everytime. Whether codes present or not. Have had no codes for quite awhile.
Recently had code P0128 and P0410. Have fixed P0128 (new tstat and sensor) and am working on P0410 (am attempting to verify solenoid function/pump works).

This condition persists regardless of codes.

Where to begin?

Mine does that same thing when < 32F. After a few seconds it drops down to the RPM as indicated on the chart provided by Roadie. As the truck warms up it will drop lower and lower until the coolant gets to around the 150-160 mark and then it will idle at 600 RPM give or take a few.

Now lets say your CTS is messed up and it reads 100 degrees cooler than it should. Then you would get consistent high RPM's even after the truck is fully warmed up.

Also, I noticed that if it is really cold outside and I am idling with the heat on full the engine will have trouble warming up fully. When the temp dips back down below the aforementioned threshold the RPM's will increase which could appear to be a throttle problem but is entirely normal for our application.
 

Sparky

Member
Dec 4, 2011
12,927
Yep mine does the same as well.
 

Mikebuild

Original poster
Member
Mar 16, 2012
4
So is it ok to shift into gear with idle that high? Back in the day, you did not shift into gear with the rpm above 1000 ... this must be different because of ???

This TB has not always idled this high upon cold start up ... it used to start at about 800 or so. It just recently jumped to 1500. Not sure why. Seams too high rpm to shift into gear.

Thanks for input!
 

CaptainXL

Member
Dec 4, 2011
2,445
Did you clean the throttle body recently or change the IAT or Coolant temp sensors?

The startup RPM ( not warmup RPM) differs depending on the temp difference between the IAT and coolant temp. From reading my Haynes manual, if the PCM detects that the coolant is within 25 or so degrees of ambient IAT temps then it will perform a cold start sequence. Which is the higher RPM one. You need to be specific what temperature it is outside and what temp the engine coolant is.
 

Mikebuild

Original poster
Member
Mar 16, 2012
4
CaptainXL said:
Did you clean the throttle body recently or change the IAT or Coolant temp sensors?

Yes ... have cleaned throttle body, but "fast idle" condition existed before ... and ... have changed coolant temp sensor as well. Fast idle exisisted before both these.

Not sure what IAT is ?

Do you agree ... not good to shift into gear at such high rpm? (+1000) ... or, are today's auto's different?

Thanks.
 

Sparky

Member
Dec 4, 2011
12,927
I always wait until the RPMs drop below 1000. Only takes a couple seconds unless it is really cold, in which case I'm outside scraping the windows off.
 

CaptainXL

Member
Dec 4, 2011
2,445
I was just outside and the temp is 75 degrees out. My startup RPM's were 1000 for about 25 seconds before dropping down to 800. I put it in gear at 1000 and noticed no harsh or ill effects.
 

Blckshdw

Moderator
Nov 20, 2011
10,696
Tampa Bay Area, FL
Mikebuild said:
Yes ... have cleaned throttle body, but "fast idle" condition existed before ... and ... have changed coolant temp sensor as well. Fast idle exisisted before both these.

Not sure what IAT is ?

Do you agree ... not good to shift into gear at such high rpm? (+1000) ... or, are today's auto's different?

Thanks.

IAT = Intake Air Temperature sensor, it's on the backside of the air intake tube by the firewall.

Mine does the same thing, every morning fires up around 1500RPM, and settles down to 800-900. Unless I'm in a hurry, I'm setting my music, windows, situating whatever stuff I'm taking with me, before putting it into gear, although putting it into gear doesn't hurt anything. By the time I get out of my complex to the first stop light, it's warm enough that it idles at the normal 600rpms :twocents:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Mikebuild said:
Not sure what IAT is ?
Many of our common acronyms have an auto-display feature. If they're underlined (except there's a bug and not all display the underline) then just hover the cursor over them and a "?" appears and then the expansion of the acronym.

View attachment 19754
 

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