2010 Silverado CC 5.3 has Blackbear tune since new .......Never did this past 3 yrs in cold weather this is a new problem
this winter when ever it started after sitting for long period, overnite etc it starts fine runs fine but idle speed stays high in gear idle when warm is 500 rpm now 800rpm and does not come off until coolant temp at least 190*F used come off fast idle around 130*

What sensor controls the cold start fast idle .....coolant temp or intake air temp or ambient or all ?? looking to change a sensor ......or could this be a TPS issue no codes truck runs fine ...... once it gets to 190 or so and fast idle comes off and turn truck off even for an hour or so when restarted the fast idle comes off normally around 130f


Had a few days of warm weather 32f plus and cold start fast idle comes off normally at about 130f but today back in deep freeze below 20f and the fast idle stays on til coolant over 190 ........ in winter my truck rarely get much over 188f unless it sits and idles alot

 

Maybe a vacuum leak?
Or sticky TB?

 

Thanks but no vacuum leaks I have a scan gage in truck and monitor that plus it runs fine once fast idle comes off ...........and I have cleaned TB( DBW) a couple of times and done a relearn after cleaning ........ hoping someone here would know what sensor or parameter the ecm uses to control cold idle speed

 

It goes off of coolant temperature.

 

Thats what I assumed but was not 100% sure since when ambient temp got over 30* fast idle comes off as normal & seems to work fine ....... easy to change coolant sensor maybe will do t-stat same time truck has 55k on it

thanks

 

It might even go off of a blend of IAT and ECT to determine the air temp entering the cylinder. I would contact Justin and see if he thinks it is an issue that could be corrected in the tune. I would start out cleaning the IAT sensor as they can get coated with a film especially if you are running a K&N or similar filter that uses an oil.

 

I have contacted Justin but he did not change the parameters for that function ........ blend of IAT and ECT it may be as it makes sense wish I could find out for sure what sensors control the fast idle anyway did not think to pull out IAT and clean , Thanks, I use a dry type cone filter no oil

 

Now that I think about it isnt the IAT built into the MAF in my 2010 5.3 the IAT is separte onanaother car I have ......so cleaning the MAF should ?? clean the IAT ?

 

I would take a look at these tables in your tune. They reference coolant temp.

 

Without having a scan of your cold idle to see coolant temp and commanded idle speed all we can do is guess. You cannot go off of the factory temp gauge as they are not very accurate. As seen above ( Factory 2010 5.3 tune) at full temp it commands 525rpm idle in gear which goes along with what you say it used to do. Its possible you have a vac. leak that once the engine gets up to temp and thermal expansion occurs it either stops leaking or is small enough that the idle under/overspeed table can correct it.