Won't Come Down From High Idle

[Mad Maxx]

The First few Times this Season when my Truck went into High Idle, it would come Off it when the IAT Reached 45* like it always has in the Past.

But now, it'll just Stay on the High Idle until I Hit the Brake. It won't come Off it any other way. My IAT was all the way in the 60's the other Day while Warming Up, and it was still in High Idle until I Hit the Brake.

Any Ideas?

 

[CtChevy427]

The First few Times this Season when my Truck went into High Idle, it would come Off it when the IAT Reached 45* like it always has in the Past.

But now, it'll just Stay on the High Idle until I Hit the Brake. It won't come Off it any other way. My IAT was all the way in the 60's the other Day while Warming Up, and it was still in High Idle until I Hit the Brake.

Any Ideas?

James are you sure the ECM uses IAT to control the high idle? I don't think it being an LBZ would be different than an the LLY. The LLY activates when the ambient air temperature is less than 32*F and the engine coolant temperature is less than 154*F. These past few days mine never come off high idle until I hit the brake and I even have the grill covered. Before this cold snap it would come off normally.

I wonder if an explanation in the owners manual. I'll have to take a look.

 

[Mad Maxx]

I Found the "Parameters" that the ECM Uses for the High Idle, and the IAT was not Listed, but I have the Insight for my Gauges, and right on the Nose, every Time, as soon as the IAT would Hit 45* it would come Off High Idle, every time.

Maybe it was a Fluke thing, but I find it Hard to Believe, that exactly when the IAT Hit 45* that the ECT would Hit 154* as well. It's Possible, but I don't think EVERY Time it would happen, one would get "there" before the other.

I'll Add ECT to the Gauge Display and See what's goin On, and let it Sit until all Parameters are "Met" and See if it comes Off High Idle by itself or Stays Stuck on it.

 

[btfarm]

I don't remember ever paying attention to when mine comes off high idle. It's been known to kick in from time to time when I have a warmed up truck sitting at the bank window or leaving it idle at a stop somewhere out by the barn in very cold (around +10* or lower) weather. I'm pretty sure it's an IAT issue in those cases. Do you have the winter grill cover on?

 

[big block 88]

IAT is not used with high idle when the temp outside is below 32 and the motor below 160F it will not idle down of either minimum temp threshold is reached.

 

[Mad Maxx]

I don't remember ever paying attention to when mine comes off high idle. It's been known to kick in from time to time when I have a warmed up truck sitting at the bank window or leaving it idle at a stop somewhere out by the barn in very cold (around +10* or lower) weather. I'm pretty sure it's an IAT issue in those cases. Do you have the winter grill cover on?

Yep, Winter Front is On.

 

[CtChevy427]

James, I copied this from a the lower part of GM document #1706150.



Elevated Idle

The engine has a cold temperature high idle feature which elevates the engines idle speed from 680 to 1200 rpms when outside temperatures are below 32°F (0°C), and the engine coolant temperature is below 150°F (65°C.) This feature enhances heater performance by raising the engine coolant temperature faster.
For pickup models, this feature can be turned off and on using the DIC steering wheel control buttons. If your vehicle is not equipped with the DIC steering wheel control buttons, do the following to turn on this feature:

Turn the ignition to RUN, with the vehicle off.
Press the accelerator pedal to the floor and hold while quickly pressing the brake pedal three times in less than eight seconds.
Release the accelerator pedal and start the engine.
When the engine is started, it will slowly ramp up to the high idle speed after a delay of a few seconds up to approximately two minutes. For this method to work properly there must be no throttle or brake pedal faults.


The engine idle speed will return to normal once the following conditions are met:


•
Once engine coolant temperature reaches 150°F (65°C).


•
Air intake temperature reaches 32°F (0°C).

The high idle speed will be temporarily interrupted and the engine speed will return to normal if any of the following conditions occur:


•
The brake pedal is applied.


•
The accelerator pedal is pressed.


•
The transmission is shifted out of PARK (P) or NEUTRAL (N).


•
Vehicle speed is detected.

Once these inputs are removed, the engine idle speed will slowly ramp back up to high idle after the normal delay, if the conditions for engine coolant temperature and air intake temperature are still met.

 

[stacks04]

In my lly tune for efi live, one of the parameters listed is IAT temp. I cant find them on the lbz stuff but they may be there and I could not find it.

 

[Mad Maxx]

Ok, here's where the Truck was at this Morning when it came Off High Idle. As you can See, the ECT Gauge in the Cluster is pretty damn far Off from Actual ECT Temp.

 

[saratoga]

Yea, the factory gauge is waaaaaay off at lower temps. The 180* mark is actually about 160* when interestingly enough 160* is the lowest marking on the gauge.

 

[Mad Maxx]

Air Temp was 35* when I Started the Truck and it still went into High Idle.

Ah well. Atleast I saw it come Off High Idle and it wasn't Stuck like I Thought. If the Truck wants to Idle Up, I'll let it.

 

[83GMCK2500]

I've had some incredibly long extended idle periods as well. I notice that they occur less frequently when I've got the winter cover on.

I had a weird one this morning, I didn't have it plugged in, went out and started it at ~30 degrees. Scraped the frost off of the front and side windows, got in and headed down the road gently. Traveled about a mile to get out of town and onto the highway, slowly accelerated to 60 and it didn't downshift. It held whatever gear that produces ~2,000 RPM @ 60 MPH. I don't know that I've ever noticed that before.

 

[btfarm]

That would be 5th w/o TC lockup. It's waiting to get warm enough to lock.

 

[RI Chevy Silveradoman]

Mine has been running until I hit the brake also. Sounds normal based on the outside temps and weather.

 

[dmaxfireman]

the ally will not lock up until the temp has warmed up. not sure on the exact temp but it is a fact fluid that is too cold is bad like fluid that is too hot. just in different ways.