Just purchased a used 2004 Envoy SLT with 51,000 km. The problem is a really loud engine noise for the first 2-3 minutes of driving. It sounds like a jet engine, or a huge air intake of some sort. This initial noise goes away after a couple of minutes and then it runs quiet. Any ideas? We have a 3 month GM warranty left on the vehicle.
I have the same problem with my '02. It happens whenever we accelerate and goes away as we back off the throttle when we reach a cruising speed (or have the cruise control set). It has been very infrequent until yesterday when it happened again and was accompanied by the service engine light coming on as well.
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You just hear it better if you lower the roof or open your windows. It could just be your air intake. Unless your rpm`s are really racing to above 2500 or it is at high idle for a long time, you shouldn't kick it down. When it is cold your choke is helping to warm it up quickly. Nothing is really working properly until it reaches normal operating temperature. Let it warm up. If you are still concerned, listen under the hood for better perspective and when in doubt, take it to a professional.
This is normal. All vehicles idle high at start up to get the engine to operating temperature. This is known as open loop. The computer ignores signals from O2 sensors to keep your engine running safely. Once it has warmed up, it will enter closed loop, and you will see a decrease in idle.
2008 GMC Envoy is only equipped with one of two engines: 4.2L (254") 6-Cylinder SFI 5.3L (325") V-8 SFI
Niether of these engines are equipped with an EGR valve, so I guess the probability of that being the cause of your noise is pretty much zero to none.
If you believe the noise is being caused by the exhaust ststem, then the only way to verify that is to inspect the exhaust system. Leaks are easier to verify with the engine running.
With that said, there is also a Technical Service Bulletin (TSB) that is published by GM that addresses customer complaints about loud noise that is being caused by the electro-viscous engine cooling fan clutch. Some people describe it as exhaust noise and others describe it as the engine "racing" or "roaring".(even though the tachometer (if equipped) will be reading normal)
It basicly says that it can make noise on startup due to high rpm of the fan which goes away once the electric solenoids open and allow the fan to start free-wheeling. GM says this is normal operation. You might want to check to be sure this is not what you are hearing. (it can be pretty loud)
If the vehicle has a clutch fan, verses an electric fan, sometimes the clutch will spin the fan too fast or at erratic speeds. I'm not saying that's what it is, but just one possible reason. Seeing how you have the warrany, I would take it in and not leave until they have remedied the problem. Let us know how everything turns out and good luck.