Cold start won’t high idle anymore

[ksack001]

2015 Silverado 1500. 1 month ago I put a carven catback, range AFM disabler and a KN air filter, there are no other mods to this truck. 4 days ago on cold start I noticed it doesn’t idle high and then come down when engine is cold, it’s starts like it’s been running all day but hasn’t. Truck sat all night last night started this morning still no high idle just started like it had been running all day. There are no engine lights on. What in the world could be causing this? 

[BO TIE 1]

Try disconnecting the range and see if that's the problem. 

[JimCost2014]

19 minutes ago, ksack001 said:

2015 Silverado 1500. 1 month ago I put a carven catback, range AFM disabler and a KN air filter, there are no other mods to this truck. 4 days ago on cold start I noticed it doesn’t idle high and then come down when engine is cold, it’s starts like it’s been running all day but hasn’t. Truck sat all night last night started this morning still no high idle just started like it had been running all day. There are no engine lights on. What in the world could be causing this? 

Maybe check your MAF and make sure it is clean, no oil from the filter, dirt, debris, anything that may interfere with it reading the incoming air.

[ksack001]

With range unplugged I have the same issue. I wouldn’t think the range would do anything to cold start idle speed. The range has been plugged in for a month. Just started having problems 4 days ago. MAF is clean, just checked. This is weird 

[MikeBMW]

38 minutes ago, ksack001 said:

With range unplugged I have the same issue. I wouldn’t think the range would do anything to cold start idle speed. The range has been plugged in for a month. Just started having problems 4 days ago. MAF is clean, just checked. This is weird 

Indeed, that is odd. I've had the AFM disabled for over 4 months (through AutoSync and BTDiesel - no need to keep the device plugged in to the OBD to save the setting) and I always get high idle on cold startup.
Maybe, depending on your exhaust, you're just not hearing the flapper exhaust valve doing it's thing on cold start?
Have you checked RPMs on startup?
I rarely do as I, generally, do a remote start nearly every morning.
I'll check tomorrow morning when I do a cold start while I'm in the truck, and see if I get an RPM rise at start-up.
I could be confusing higher idle with the sound of the exhaust flapper doing it's thing.
I dunno, but worth a look to see if it's connected to your issue.

Edited September 3, 2021 by MikeBMW

[JimCost2014]

1 hour ago, MikeBMW said:

Indeed, that is odd. I've had the AFM disabled for over 4 months (through AutoSync and BTDiesel - no need to keep the device plugged in to the OBD to save the setting) and I always get high idle on cold startup.
Maybe, depending on your exhaust, you're just not hearing the flapper exhaust valve doing it's thing on cold start?
Have you checked RPMs on startup?
I rarely do as I, generally, do a remote start nearly every morning.
I'll check tomorrow morning when I do a cold start while I'm in the truck, and see if I get an RPM rise at start-up.
I could be confusing higher idle with the sound of the exhaust flapper doing it's thing.
I dunno, but worth a look to see if it's connected to your issue.

Cold start should jump up to around 1250(?) or so, then slowly work its way down to the normal 500 in a few minutes.

Edited September 4, 2021 by JimCost2014

[MikeBMW]

1 minute ago, JimCost2014 said:

Cold start should jump up to around 1250(?) or so, then slowly work its way down to the normal 500 in a few minutes.

Thanks, Jim, I look for that in the morning.

[JimCost2014]

Just now, MikeBMW said:

Thanks, Jim, I look for that in the morning.

You are very welcome.

 

Know it is more than a 1000 RPM, but don't think it exceeds 1500 RPM.

[ksack001]

Yeah it def jumps up on cold starts and works it’s way down as it wants up, not sure of exact idle speed but it’s not doing that at all anymore. On cold start it’s idling at normal idle speed after sitting all night. 

[MikeBMW]

2 minutes ago, ksack001 said:

Yeah it def jumps up on cold starts and works it’s way down as it wants up, not sure of exact idle speed but it’s not doing that at all anymore. On cold start it’s idling at normal idle speed after sitting all night. 

Do you have a scan tool to check codes and, maybe do a DTC clear?
Might help for a bit, or for a long time if it's just a legacy code triggered which might be causing the behavior.
Again, I'll update in the morning for my truck.

[ksack001]

There are no codes at all. I unplugged the battery for 10 min and plugged it back in we will see in the AM. 

Edited September 4, 2021 by ksack001

[MikeBMW]

21 hours ago, ksack001 said:

There are no codes at all. I unplugged the battery for 10 min and plugged it back in we will see in the AM. 

Checked mine today.
As @JimCost2014 mentioned, 1200 RPM at startup with a slow decrease to about 500 RPM.
Not sure why you aren't seeing this.

[rlcole321]

The Batt needs to be disconnected for a min. of 3 hours to clear memory.

[sic02ss]

old thread but mine just started not high idling. did you ever figure it out?... My battery is starting to go, had it tested and its holding charge but fails cranking, im wondering if that has something to do with it? Its been hard starting when warm and once it wouldnt turn over at all and when i jumped it my station presets on the radio wouldnt show up, the radio preview in the gauges wouldnt show anything, and service trailer brake system warning came on... let it sit and tryied it again and after the 2nd time it was back to normal which is what is making me think its just the battery not feeding enough voltage to something in the start-up process, not sure though.....  

[AR10]

If that does not beat all. My 2018 5.3 litre never idled high at start until a week ago after changing water pump. Now I'm confused, was it not working correct before or is it not correct now? I don't like the high idle.