Question about 2004 GMC Envoy

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Engine idles up and down. heater controls don't work

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Hello hear your having idle issues well the first guy don't know sh-- you need to look at your idle air control this is more than likely the culprit on this let me know if you are wondering were it is follow your air cleaner piping to the engine there were the clamp holds the pipe to to engine for air it's right there there should b 4 sensors on the throttle body the best way to know which one is look at the part then you can definitely know what it looks like regards Chris ...

Posted on Mar 19, 2014

  • Christian Krentz
    Christian Krentz Mar 19, 2014

    Also try to hear for a vacuum leak your heater controls run off vacuum


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Check for codes. Sounds like its hunting, check for vaccum leaks, clean TB and MAF.

Posted on Mar 19, 2014

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Where is my heater control valve located on my chevy 1500 WT 4.3 2 wheel drive pick up Im not getting any heat unless riding down road when I stop it blows cool untill I start driving again

Chevy vehicles do not heater control valves in the water lines any more...they always rust out and malfunction. What you are probably experiencing is a bad vacuum ball or a vacuum tubing leak in the heater box area under the dash. The control lead that you use to adjust the heater (temp and direction), is vacuum controlled from engine vacuum. Engine vacuum varies under load and at idle, so the manufacturer put vacuum balls under the dash to store vacuum for the controls. When you adjust the heat or direction, vacuum from the balls is diverted to vacuum motors that position the blend doors to pass air thru the heater core or A/C evaporator. Other motors direct their door(s) to position the air to the floor, mid-vents, or to the defroster. A leak in the tubing, ball, or motor can cause the door(s) to retract to default if vacuum drops down as it does at idle. Have the heater box and vacuum system to it checked out.

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It likely has EFI (electronic fuel injection) and an idle air control valve that regulate idle speed. They can get gummed and fail to have a fast idle when cold, or get stuck the other way, and have a too fast idle all the or regularly take its time slowing down after you take your foot off the gas. An engine temp sensor can also cause a lingering high idle if it reports the engine as still being cold after warm up.

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Rev below 500rpm on idle, engine dies

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My Chrysler 300m (2004), has been overheating, thermostat replaced, new radiator, mew at a loss. it only overheats while idling or in traffic.

Have your hose's checked , Sounds like your hose may be collapsed, this happens when breaks down from presure. Is this don't work JUst turn your heater on and let idle if this keeps from getting hot your heater core is stopped up. Best of luck, Let me know hao it go's,

Apr 13, 2011 | 2004 Chrysler 300M

2 Answers

When the car is idling, the heater blows out cool air but when the car is moving, the heater works fine

When the coolant in the heater core is hot from the engine and your fan is on hot air will blow through the hot fan coil, i figured it out, when i stepped on the gas i could here the coolant squeezing by the control or limiter valve, because the higher rpms make the belt spin faster which makes the water pump pump harder causing more pressure, so when u idle that hot coolant will cool down from the fan blowing on it, u need to find the control valve and open it up to full blast, then hot coolant will always be flowing through your heater coil. ;)

Dec 17, 2010 | 2008 Pontiac G6

3 Answers


Check the heater core for a clog or the heater control valve. The easiest was to check these is allow heater to run for a few minutes and check the two hoses coming from under the hood against the fire wall. They should both be hot. If they are not, you have one of the above problems. Start with the heater control valve and replace it. It is much cheaper than than a heater core. Next, you will need to pull the lines from the firewall and see is rust starts coming out of the lines, if so, you may be able to flush the system and clear the blockage. After that, if it does not work, it will require replacing the heater core, which is no easy or cheap feat.

Let me know if there is anything more I can help you with.

Please remember to rate this solution.

Sep 24, 2008 | 1999 Ford Taurus

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