I don't recommend relying too much on the computer diagnosis, as several factors can cause the same symptoms. If you have not been using a fuel injector cleaner regularly in your fuel, you could have dirty fuel injectors. If that is the case you will, most likely, have to have them manually cleaned or replaced.
Also, is your air filter dirty? Something this simple can cause the symptoms you describe if it is blocking too much air from getting to the engine. I'm not quite sure what your friend meant by "carbon build-up in the engine". With regular oil changes (especially with full synthetic oil) this very rare with modern engines.
Finally, are the spark plugs over 100,000 miles old? All modern domestics can now go a minimum of 100,000 miles with the factory spark plugs. If yours are the original plugs, this could be the problem. Before spending a fortune at a shop, I'd try a few very simple and inexpensive things first.
1) Check the air filter. If it is very dirty, put in a new one.
2) Put 2 or 3 cans of fuel injector cleaner and 1 can of 104 or 108 Octane booster in the gas tank with it about half full. Drive the car pretty hard (fast acceleration, high speeds alternating with slower speeds) until it needs more fuel. If the fuel system is dirty this can possibly clean it sufficiently to save you a manual cleaning (pricey at most shops).
Lots of luck. I'm a mechanic, and two good friends of mine have experienced problems similar to yours. One had a Hyundai Accent and one had a 2003 GMC 6. Neither had been regularly using fuel injector cleaner in their gas. In both cases the treatment suggested in point number 2 above solved their problems without expensive engine repairs. I hope this may be the case with yours. I've found the I-6 GMC Envoys to be one of the most reliable and durable SUV's on the road.
I posted a comment on Dec 16th (16:12). Well, I have solved my problem with my car. It turned out the catalytic converter was causing all of the problems. With the problem fixed my car runs great.
We have a 2003 Envoy SLT with 111,000 miles on it. Last night, 5 1/2 hours into our trip home with about 1 1/2 hours left to go, our Envoy would rev the rpms up to 3 then drop to about 1 1/2,then back up and down while going down hill and only downhill. The vehicle would not accelerate, it only seemed to be in revving noise and showing on the rpm gauge what it was doing. It almost sounded like our cooling motor, but the rpms were affected. Anyone else have this problem?
I have a 2003 Envoy XL and I have the clicking noise, I've had it for a year or so. I don't drive the car much, but I'm selling and would like to know how much it is to replace the fan clutch? Also does anyone know how much it is to recalibrate the PCM (don't know what that is, but on other post they said I should do that first).
I have a 2003 GMC Envoy SLT. I've replaced the clutch fan and now it sounds horrible. The check engine light keeps coming on and then off too. Now this morning I was at a stop light and it just shut off. I was able to restart it, but am wondering what's going on. It goes to the garage today.
Have a 2003 Envoy SLT with 104,000 miles.
Replaced gas tank in Jan 2010, now need water pump, fan clutch, thermostat.
The dealer did replace the tank under a special policy, but I am still going to be out of about 1500 plus. Piece of junk.
Also my sunroof is leaking, heated seats are out on the driver's side, and my mirrors and seat have to be reprogrammed all the time.
I bought a 2006 Envoy two years ago as a certified vehicle. I have always bought certified vehicles, which gives me peace of mind.
Yesterday I was driving when my stabiitrak light came on, as well as the check engine and the emission light. The car completely shut down. I waited a minute or so, and the car started right up. When I got home, checked my gas cap and tighten it up, all the lights went away.
Today whilst driving, my car did the same thing, and two more times on the way to the mechanic. This could be very serious if I was on the freeway. Anyway, I was told it was my computer system at the tune of $700.00. It seems that a 4 year vehicle should not have this happen, anyone else have this problem?
I research all my vehicles meticulously before buying them. I found that a major problem with the Trailblazer/Envoy/Rainier series was the computer, and that the MAJOR source of trouble was untrained service techs that screwed up the computers. I sought out a dealership that had special GM-certified computer technicians on staff.
We bought a 2003 Envoy new in early 2003 and it has been absolutely flawless. It just turned 90,000 miles and thus far it has had one battery, one set of tires and NOTHING else, not even a brake job.
We had one minor, computer caused glitch early on, and the dealer service techs fixed it and it has been perfect ever since. If I am not mistaken, you can buy the computer for under $200 at AutoZone (or other parts stores) and installing it is really quite easy. Lots of luck.
I'm sorry you are having problems with your Envoy. My wife's best friend bought one based on our good experience and hers has been flawless as well. These are very safe, and generally very reliable vehicles. My brother-in-law gave his Trailblazer to his son at 165,000 miles and bought a new Trailblazer. The old one has over 200,000 miles now with never a repair.
I just fell in love with a 2003 Envoy on sale at a local used car lot, and came here to do some research. It's the metallic red all-dressed model with 145,000 km for $6000CAD.
I'd like to thank all of you for posting so many details concerning the problems with this truck. Needless to say, I will be staying away from this "deal". Too bad though, it was exactly what I wanted in a truck, except without all the problems and hassles.
Now I don't know what to go for. I can't afford new, and haven't seen something even close to the 8 passenger Envoy.
My wife and I, our best friends, and three of our family members have had absolutely flawless service from the GMC Envoy and Chevy Trailblazer (these are the exact same vehicles). One of them now has 165,000+ miles with never a problem, and my wife's has 90,000 and has had absolutely NOTHING done to it, not even a brake job.
The Trailblazer, Envoy, Buick Rainier, Olds Bravada and Isuzu Ascender are all the exact same vehicle marketed under different brand names. One of our neighbors just found a like-new 2005 Olds Bravada at a great price with only 100,000 miles on it. They LOVE it. These cars are very smooth, very fast and reliability on every one that we know of has been really great. I don't know of anyone who has had any problems with one of these before 100,000 miles.