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2002 chevy trailblazer_ls
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Discussion Starter #1
Hi, I own a 2002 trailblazer 4.2 4x4 that has really poor acceleration and power. I have changed plugs, o2 sensor(upstream), air filter, fuel filter, oil, & transmission filter. Also put some fuel system cleaner in my last fill up. When I changed the plugs I decided to clean the throttle body. I read somewhere that with electronic throttle bodies not to manually move the butterfly. So, I turned the key on (didn't start engine) and put a big brick on the gas petal. The butterfly barely opened at all. Also heard a quiet high pitch tone or like beep sound coming from the throttle body. My question is shouldn't the butterfly open further? I assumed it would open all the way. Mine barely moved maybe 1/2 to 1 inch of movement. Also when I took the brick off the gas petal I was able to walk around to the front of the vehicle before it closed. As you know the units are expensive. Is this normal or do you think the throttle body is bad? Thanks.
 

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2002 chevy trailblazer_ls
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Discussion Starter #2
no check engine light

My check engine light doesn't work. Not sure if the bulb is blown or been removed. Autozone says I have no codes stored.
 

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2002 chevy trailblazer_ltz
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When you cleaned the TB,did you take it off and clean both sides and move the butterfly to see if it opens up easy and did you do a reset?
 

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2002 chevy trailblazer_ls
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Discussion Starter #4
yes

Yeah I took it off. Cleaned it all really good. The butterfly moved easily before and after I cleaned it. Yeas, I also reset.
 

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2004 gmc envoy_sle_xl
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I'm pretty sure the butterfly will not make a full travel with the engine not running, it is controlled by the PCM not solely by the accelerator pedal.

As far as your lack of power, maybe you have a clogged catalytic converter. Try removing the uostream O2 sensor (on the exhaust mainifold) and see if your performance improves.

Also, get that check engine light fixed, if you don't know when a fault happens, you can destroy the catalytic converter before too long.
 

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2002 chevy trailblazer_ls
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Discussion Starter #6
remove upstream o2?

So, if the performance improves without the sensor would mean clogged cat converter?
 

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2002 chevy trailblazer_ls
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Discussion Starter #7
you did mean upstream o2 and not downstream? Is there a way to clean/unclog cat converter? Or would I have to replace it?
 

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2004 gmc envoy_sle_xl
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Upstream O2 sensor, on exhaust manifold. Can't repair cat, only replace.

Also need to find out why it clogged. Is your operating temperature too low? Should be at or near center mark on temp gauge.
 

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2004 gmc trailblazer_lt_ext
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The throttle position sensor is connected to the throttle plate shaft and monitors the position of the throttle. The throttle position sensor sends a signal electronically to the power control module. The position of the throttle plate shaft changes when the car is idling, at full throttle or at part throttle.
 

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2003 chevy trailblazer_ls_ext
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Testing sensors?

How do you test the throttle position sensor? I have and '03 TB with the same issue. Mine runs great idling and cruising but doesn't want to accelerate well, most noticeably when going up hills. Everything I can think of has been checked and done. New fuel pump, fuel filter, ac delco plugs, thermostat, trans filter(fluids looked great), checked CC by removing upstream o2 sensor(did not improve).
Running out of ideas! Could it be one of these sensors and how do I check them?
 

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2004 chevy trailblazer_lt
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Also need to find out why it clogged. Is your operating temperature too low?
Jon, Freddy points this out due to the engines needing to stay at operating temp. A fouled thermostat that won't let the engine up to 190+ will cause the cat to clog. Get your engine scanned (assuming you don't have a scan tool yet), and check the high temp reading when hot. The gauge is a reference, and vertical is around 195 to 205 (sometimes 210).

Good luck!
 

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2002 chevy trailblazer_ls
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Discussion Starter #12
removed o2 sensor

I took the trailblazer for a spin after removing the o2 sensor. Didn't see an improvement maybe just a little. It was definitely louder. Anyone else have a clue what might be wrong? Feels like it struggles up hills and even on level ground between gears. Not much power.
 

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2002 chevy trailblazer_ltz
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You really need to hook it up to a unit that shows live info,to see if all cylinders are firing,O2 circuit is working etc.
 

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2004 chevy trailblazer_ls
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Here is your problem for power loss

I have been chasing the lack of acceleration and sluggish I6 for way too long. The issue is a vacuum leak, that no one has seem to of found. I have seriously replaced everything on my TB '04. Never could find the secret vacuum leak. Well I found it and yall will not believe it, but I think your gonna love me. I tested the entire side of the engine. NO vacuum leaks. I tested the brake booster. it held at 20-21 psi (I think that's right, from memory) Never did I test the brake booster check valve. Why would I? We its a very cheap part, so I changed it. My TB runs like a champ. For over 2 weeks now, I have not had any power issues or stumble. All power and acceleration has come back and she runs like she is new. Even brakes and stops like it was new. The reason for the brake booster check valve causing the vacuum leak is this. It is supposed to be a one way valve. It holds the pressure for your brake booster but the valve can get weak or fail. So it either wont seal or stays sealed or open. I don't know what mine was doing, but it sure was not doing its job. I LOVE my TB again. I really hope that I help someone. I could not keep this to myself. I know how many people are out there that have lost their mind over this loss of acceleration and sluggish, junk. I know that a brake booster check valve sounds crazy, but its @ $11-$20 on amazon. Its insanely easy to swap out. No reason not to give it a shot. I seriously was about to take my TB into the transmission shop because it wasn't shifting right or stopping right. I also already have a new brake booster and master cylinder, ready to go, but this little valve solved SO SO many issues.

Just FYI:
My part number for my 2004 LS trailblazer I6 is: ACDelco 179-1266
 

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Same issue

I have the same issue with my 2005 TrailBlazer 4.2L. Poor acceleration and no power. Code 2119 came up so I changed the throttle body assembly and the accelerator pedal assembly. Nothing worked. Did you guys have been able to fix the problem. Can it really be the brake booster check valve ? Please help me I'm running out of ideas and about to bring my TB to the scrapyard!
 

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2006 chevy trailblazer_lt_ext
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197 Posts
No, the brake booster should not have anything to do with this DTC. P2119 sets when the PCM does not see the throttle plate returning to "default" when the PCM goes to sleep. I'm proceed assuming that there are no other DTC's set. Please advise if this is inaccurate.

First, please check and record battery voltage across the terminals with a digital meter. You'd be surprised how modules freak out when battery voltage is a little off.

Do you have a scan tool that can view the throttle position? If so, follow this procedure:
1) Turn key off for 15 seconds
2) Turn key on, engine off (KOEO) for 20 seconds
3) Record the indicated throttle position PID on the scan tool

In the meantime, remove the throttle body assembly and inspect for obstructions that would prevent the throttle blade from returning to default position.

If you report back with your findings, I can guide you further down the diagnostic procedure for this DTC.
 

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I cleaned the throttle body so there's no obstructions. The battery voltage is ok. Now there's a new problem : the shifter is stuck in park (the shifter button won't engage) or the key is stuck in ignition and won't turn off. Maybe it's an electrical problem, like a bad ground.... And I don't have any scan tool to check the throttle butterfly position.
 

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2006 chevy trailblazer_lt_ext
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197 Posts
Well that's a seperate problem in the shift interlock circuit.

Here's what I'm going to recommend: take the vehicle to a reputable repair shop in your area and pay for an hour's worth of shop time to diagnose one or more specific problems. Even if you elect to perform the actual repair yourself, you'll be dollars ahead in the long run. Without an OE level scan tool, it's pretty close to impossible for the DIYer to property diagnose these kinds of issues. All of the shade-tree things of yesteryear do not apply to modern vehicles. You can continue to shoot the parts cannon at the car based on what people tell you, but I guarantee you'll run out of money before you run out of guesses.

Best of luck.
 
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