2004 trailblazer

Hey all
My friend has a 2004 Trailblazer with a 4.2. He was driving it a few days ago and the check engine light came on and it would not run pass 15 miles per hour. He turned the truck off and re-started it. The light went off and the problem went away. The scan tool came up with an old code that that throttle body sensor was bad or the throttle body needed cleaned. We cleaned the throttle body and ran it and it ran fine. Now here is the problem. When the heater is on and the truck is at idle, the truck will idle at 2000 rpm, then kick back to normal then kick back to 2000 rpm and then keep repating this issue. If we shut the heat off, the truck idles fine. Any ideas?

if this is a drive by wire....there is a idle learn reset with a enhanced scan tool.or a manual one...
Without Scan Tool-Learn


The engine speed is between 450-4,000 RPM.
The manifold absolute pressure (MAP) is greater than 5 kPa.
The mass air flow (MAF) is greater than 2 g/s.
The ignition 1 voltage is greater than 10 volts.
Start and idle the engine in Park for 3 minutes.
With a scan tool, monitor desired and actual RPM.
The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
Ignition OFF for 60 seconds.
Start and idle the engine in Park for 3 minutes.
After the 3 minute run time the engine should be idling normal.
Important: During the drive cycle the check engine light may come on with idle speed (http://www.alldatadiy.com/alldatadiy/DIY~V41171938~C44783~R0~OD~N/0/128809663/130923470/133596388/133596390/34853741/34857029/34858641/58800534) DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.



If the engine idle speed (http://www.alldatadiy.com/alldatadiy/DIY~V41171938~C44783~R0~OD~N/0/128809663/130923470/133596388/133596390/34853741/34857029/34858641/58800534) has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.

if this is a drive by wire....there is a idle learn reset with a enhanced scan tool.or a manual one...
Without Scan Tool-Learn


The engine speed is between 450-4,000 RPM.
The manifold absolute pressure (MAP) is greater than 5 kPa.
The mass air flow (MAF) is greater than 2 g/s.
The ignition 1 voltage is greater than 10 volts.
Start and idle the engine in Park for 3 minutes.
With a scan tool, monitor desired and actual RPM.
The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
Ignition OFF for 60 seconds.
Start and idle the engine in Park for 3 minutes.
After the 3 minute run time the engine should be idling normal.
Important: During the drive cycle the check engine light may come on with idle speed (http://www.alldatadiy.com/alldatadiy/DIY~V41171938~C44783~R0~OD~N/0/128809663/130923470/133596388/133596390/34853741/34857029/34858641/58800534) DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.



If the engine idle speed (http://www.alldatadiy.com/alldatadiy/DIY~V41171938~C44783~R0~OD~N/0/128809663/130923470/133596388/133596390/34853741/34857029/34858641/58800534) has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.


Thanks so much. I have a Genesis. How do I know if this is a drive by wire or not?

If there is no throttle cable to open the throttle plate, it's drive by wire.

this is a drive by wire......the relearn i lsted above is for newer trailblazers.....i dont know if it works on a 2004.look in the genesis for a idle learn.if not maybe just driving it it will learn.

I would clean the throttle plate and bore......then disconnect the negative and positive battery cables......now hold the cables together for one minute.....then reconnect the pos and then the neg cables.....

As for that code, check the harnesses, especially the female connectors for looseness.....a drag test with a male connector is the correct way....