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2003 chevy trailblazer_ls
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Discussion Starter #1
I have a 2003 Trailblazer. We replaced all the plugs, ignition coils, and removed the throttle body and completely cleaned both sides. The vehicle appeared to run smoothly until it warms up, about 30 minutes of driving. Now it accelerates on its own and is very hard to brake and stop. Once stopped the suv idles rough and seems like it is going to stall. The suv attempts to keep going causing hard braking until about 5mph when it stops the acceleration all at once making the suv brakes to lock up from all the pressure being applied to stop. Once moving forward again, the idle takes over and accelerates endlessly. I allowed it to go to see just how much it would accelerate and I started to apply the brakes once the suv broke 55mph. While coming to a stop I shifted to nuetral so I wouldnt be fighting against the engine and the RPM's shot up to 4k and were increasing until I placed it back in gear to prevent damage from the high RPM's. Does anyone have any idea what is going on?
 

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2003 chevy trailblazer_ls
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Discussion Starter #2
Not "Solved"

By the way this problem is not "solved". It would not let me post without a prefix and the only prefix it allowed me to place is "solved". Any help would be greatly appreciated...............thanks.
 

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2008 chevy trailblazer_ls
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40 Posts
I am no expert nor claim to be one but it seems like it may be the computer making it run at such high RPMs. If you haven't already, I would strongly suggest unplugging the battery for AT LEAST 30 minutes and let the computer reset itself and then take it for a spin. Report back and let us know what it does the next time you drive it.
 

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2002 chevy trailblazer_ltz
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3,250 Posts
....it may be the computer making it run at such high RPMs. If you haven't already, I would strongly suggest unplugging the battery for AT LEAST 30 minutes and let the computer reset itself .....
Since you'll have the battery disconnected (and I recommend at least 35-40 minutes), you might as well remove the throttle body from the engine and give it a good cleaning, unless this has been done VERY recently.
 

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2003 chevy trailblazer_ls
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12 Posts
Discussion Starter #5
Update

I removed both the positive and negative cables to the battery for 3 hours. I then hooked everything back up and started the vehicle and just let it idle for 20 minutes. About an hour later I took it for a drive first through residential streets(about 10 miles or so with many stops) then onto the highway. The suv seemed to drive as normal until exiting to turn around after 20 minutes of highway driving. When getting back onto the highway I could feel the vehicle surge back and forth and watched while the RPM's would drop from 1500 to 1000 back and forth. I stayed on the highway for an additional 15 miles and when I exited and came to a stop, the suv died. I restarted and found the vehicle losing power and stuttering. The vehicle died a second time when slowing to make a right hand turn. I didnt experience the high idle as before but the suv struggled to make it home. It did seem to run smoother when I killed the a/c but still studdered a lot the rest of the drive home. From a stop, it would almost die when I first stepped on the gas then would surge forward until the next stop when it would repeat. Any ideas?
 

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2008 chevy trailblazer_ls
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40 Posts
Not the update I was hoping to hear. It maybe the fuel pump, hopefully someone on here with more knowledge can offer some more suggestions.
 

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2008 chevy trailblazer_ls
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Any updates, are you still having the same issues? It's a shot in the dark but you may want to try a bottle of Techron, Lucas or other fuel system cleaner. Some say they are a waste of money but I alternate between Techron and Lucas every few months. It may be something like clogged fuel injectors or something that a bottle of fuel system cleaner may fix or improve, worth a shot IMO.
 

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2003 chevy trailblazer_ls
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12 Posts
Discussion Starter #8
Nothing new

No new updates yet. I plan on cleaning the TB again and trying "Lucas" to see if I have any better results.
 

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2006 chevy trailblazer_ls_ext
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3 Posts
Try a new gas pedal. These vehicles do not have a throttle cable. Take the throttle pedal off and inspect it for any damage. Also smell it for any burnt smells.
 

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2003 chevy trailblazer_ls
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Discussion Starter #10
Update

Finally I had a chance to reclean the tb. I disconnected the negative terminal during this process. After reassembling I took it out for a test drive. First thing I noticed was the A/C would only blow out the floor vents or the defrost vents. The vehicle performed flawlessly for the first 20 minutes other then the A/C not blowing out the dash vents. I drove it both residential then highway. After about 20 minutes and exiting the highway the vehicle started to surge and lose power. With the accelerator steady it would drive fine then lose power dropping 5 to 10 mph then drive normal again for a short distance until repeating the process. It never acted like it wanted to die and it never accelerated on its own..................Ideas from anyone? Could this be a bad accelerator pedal sensor or a PCM issue? Any and all ideas or suggestions from anyone would be helpful. By the way when I stepped on the gas, it would take off like the wind.
 

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2008 chevy trailblazer_ls
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40 Posts
Interesting, I'm having a somewhat similar situation after I cleaned the throttle body. My AC works fine and it doesn't idle rough but rpm's fluctuate when coasting. All was fine until I cleaned the TB the first time. I've cleaned it numerous times and even had the PCM flashed. I've posted the problem in detail before but no luck in finding the problem yet.
 

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2003 gmc envoy_slt_xl
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10 Posts
Envoy 2003

Hi guys!! I've the same problem with my envoy, any idea for this issue? I'll appreciate it!!
 

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2004 chevy trailblazer_ls
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2 Posts
Same issue here...was told to check my cat converter. I just had that checked and it was not clogged. I have changed the fuel filter (ok), check fuel pressure (ok), cleaned my throttle body and was told I have the latest computer update. I was advised today to change my upstream O2 sensor. If no change, replace the throttle body. The Throttle Body has sensors that can go out. any other advice?
 

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2003 chevy trailblazer_lt_ext
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5 Posts
I used to work for a dealer rare but have seen a power brake booster leak never on a tb and that would not show with a smoke test I personally don't like the smoke test I prefer carb cleaner and listen for change in engine speed but be carefull if you use the carb cleaner and best of luck maby you will get luck and get some codes
 

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2003 chevy trailblazer_ls
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525 Posts
A clogged cat will not cause the symptoms the OP is having, instead it will give poor acceleration etc. I had a similar issue but my idle did not make it up to 4k. It did however idle rough at times and almost stall then the idle would jump to about 1k-1200 rpm. It was the cam position sensor located on the front of the engine near the CPAS. Your A/C issues may be an actuator door that failed when you reconnected the battery. They go through a reset process during reconnection and unfortunately fail sometimes.
 

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2003 chevy trailblazer_ls
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12 Posts
Discussion Starter #18
Finally some results

After several test drives and recleaning of the throttle body to no avail, my trailblazer finally gave me a sel. The codes given were P0171 and P0172. I replaced both oxygen sensors and all of my loss of power, surging power, and rough idle/stalls have come to a halt. The upper O2 sensor was very easy to change out but the lower one behind the cat was a job. The electrical connection was tough to reach and a pain. Removing the sensor from the exhaust pipe was very tough as I was unable to break it free using only muscle power. I ended up using a rachet tie down connected to the frame and once I had maximum torque applied to the rachet connection, I used a hammer to strike the socket drive and broke it free. Now the only thing left is to fix the a/c so it blows out of the dash vents and not the floor and windshield vents. I am sure this has been discussed somewhere on this forum but if anyone wants to give me some help, it would be greatly appreciated. BTW I purchased both O2 sensors and the O2 socket for 139
 

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2003 chevy trailblazer_ls
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12 Posts
Discussion Starter #19
One more thing

After inspecting the two old O2 sensors, the upper O2 sensor looked very bad and charred while the lower O2 sensor was a ton cleaner. If you are tight on money I would try replacing only the upper O2 sensor first and see if this fixes the problem before spending the additional money on the lower O2 sensor
 
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