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2002 chevy trailblazer_lt_ext
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6 Posts
Discussion Starter #1
I have a 2002 TB LT EXT with 155000 miles on it. The engine idles low, is very rough, and if I just barely touch the accelerator the engine stalls or at least hesitates when parked. It will also stall on its own when stopped at a light. Having the AC on seems to make it worse, but it will happen with the AC off too. After joining and reviewing the site I performed the following maintenance- Cleaned the throttle body, changed the plugs (with 41-103s) and changed the fuel filter. The fuel filter was not the OEM filter, but it was replaced anyway. I had the filter mount without a metal strap / screw. It was held in place by a single wire tie. The plugs looked like they were the original plugs- old style Delco logos and nearly no electrode left. TB was dirty but not as bad as I expected. I was unable to figure out how to remove the electrical plug, so I left it connected and cleaned the thing in a pan as it sat on top of the engine. What's the trick to the plug anyway?

So after a couple of wonderful evenings spent bonding with my young son and the 'blazer, the engine still behaves the same way except it doesn't stall when stopped. It still hesitates in park when the accelerator is lightly depressed and it still idles low and roughly. I'm hoping there is a sensor (O2?) that might need cleaning or replacement, but I have no engine lights or warnings / codes. The engine seems to be smoother while driving, accelerates a bit better (no thrill ride here though- the L6 pushing that ride does not equate to woo-hoo!) and in general the vehicle runs better. So how do I fix the idle hesitation / roughness? I figure I've saved myself several hundred bones following advice from TrailVoy, so this is my cry for help!

Thanks-
Bill
 

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2002 chevy trailblazer_lt_ext
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6 Posts
Discussion Starter #3
Affirmative- both when I did the TB / plugs and when I did the filter the next night. Thanks for your quick response. Any other ideas?
 

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2004 gmc
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26,181 Posts
If you missed doing the plugs at 100K miles, I gotta ask why? Other maintenance like changing the coolant at 100K is important, but I have to admit probably isn't related to this problem.

The upstream O2 sensor is also a candidate to change unless you have a scan tool that confirmed the data coming out of it was proper, make sure to use a Delco. And the camshaft position actuator/solenoid is also a suspect - it could have jammed or gotten clogged oil screens. Sometimes we use the acronym CPAS for that item, and a search will find the threads about changing it out.

And definitely Seafoam for the cylinder carbon buildup and maybe a couple containers of Techron in the fuel tank for the injectors.
 

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2002 chevy trailblazer_lt_ext
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6 Posts
Discussion Starter #6
Regarding the plugs, the sitch is simple- the vehicle was driven by an ex-sister-in-law and I simply don't have a way to know for sure what was done and what wasn't done maintenance-wise. Plugs seemed cheap, relatively simple, and as it turned out they definitely needed replacing. BTW I sold the mileage short- the thing has 158000 on the odo.

Can someone amplify the Seafoam advice? I'm familiar with the brand, but which product would help with the issues I've got? Please advise. The 02 sensor seems like a potential culprit, so I'll probably tackle that as well. After that the CPAS would be next I guess. Would that be the most logical R/R sequence? I'm no mechanic but I have this awesome set of tools!

Thanks again-
Bill
 

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2002 chevy trailblazer_lt_ext
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Discussion Starter #9
It's been a while, and a few things have been fixed. I just wanted to see if the braintrust might have some more ideas for me.

The engine running rough was the first thing we noticed. We discovered that when the transmission was replaced the engine mounts were somehow damaged or improperly installed. The engine running rough was caused by that. New mounts = smooth engine. Silky smooth for a vehicle with 160000 less-than-kind miles on it.

The SES light kept coming on though, and we found out that this had been happening for years, even before we started maintaining the vehicle. The dealer had been unable to diagnose the issue for the entire time. I researched the code (P0442) and found out about TSB 05012 (Google it). It turned out that the gas tank had what amounted to a known defect and the tank was replaced by the dealer at no cost to us. SES = out and inspection passed. Finally!

The vehicle still stalls though. It actually stalled on me while I was driving the other day, which sucks in a particularly menacing way. The stalling is unpredictable and doesn't seem to be affected by AC, temperature, weather, or anything else I can determine. It will stall sitting at stoplights and it will seem to "bog down" while driving at low speed with low engine RPM, like driving 30 through my neighborhood. The only things I haven't done now are Seafoam and the camshaft sensor. Does anybody think the camshaft sensor is to blame for the stalling? There are no codes any more...the new tank cleared those out. The dealer (predictably enough) is unable to diagnose the stalling.

I'm a bit reluctant to try Seafoam, but I could be talked into it...

Thanks!
 

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2003 gmc envoy_slt
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2,903 Posts
I would do the seafoam it's the easiest.Have you checked the fuel pressure regulator ? mine had a leak and was putting gas into the housing before the throttle body.
 

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2004 chevy trailblazer_ls
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256 Posts
Probably a very dumb question but wasnt listed in things done but what about air filter?

As for the plug on the TB, I just did mine as well recently and theres a grey slide lock on the plug you pull out some. I used a small flat head screw driver to hook it and pull it out to unlock it then the plug came right off.
 

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chevy
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1,091 Posts
Change the Camshaft Position Sensor. My truck was doing the exact same thing yours was every so often. It wouldn't set the CEL but the PCM was storing a pending fault P0014. CPS changed = problem gone.

CPS = the small sensor underneath the front cover. Not the large one a little farther back on the passenger side of the head.
 

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2006 chevy trailblazer_ls
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1 Posts
clean

It's been a while, and a few things have been fixed. I just wanted to see if the braintrust might have some more ideas for me.

The engine running rough was the first thing we noticed. We discovered that when the transmission was replaced the engine mounts were somehow damaged or improperly installed. The engine running rough was caused by that. New mounts = smooth engine. Silky smooth for a vehicle with 160000 less-than-kind miles on it.

The SES light kept coming on though, and we found out that this had been happening for years, even before we started maintaining the vehicle. The dealer had been unable to diagnose the issue for the entire time. I researched the code (P0442) and found out about TSB 05012 (Google it). It turned out that the gas tank had what amounted to a known defect and the tank was replaced by the dealer at no cost to us. SES = out and inspection passed. Finally!

The vehicle still stalls though. It actually stalled on me while I was driving the other day, which sucks in a particularly menacing way. The stalling is unpredictable and doesn't seem to be affected by AC, temperature, weather, or anything else I can determine. It will stall sitting at stoplights and it will seem to "bog down" while driving at low speed with low engine RPM, like driving 30 through my neighborhood. The only things I haven't done now are Seafoam and the camshaft sensor. Does anybody think the camshaft sensor is to blame for the stalling? There are no codes any more...the new tank cleared those out. The dealer (predictably enough) is unable to diagnose the stalling.

I'm a bit reluctant to try Seafoam, but I could be talked into it...

Thanks!
try cleaning tha mass air flow sensor but use the cleaner from the part store. its call mass air flow sensor cleaner its like 8 bucks. also take the air duct from the throttle body and clean the throttle body out with some intake cleaner. use something to push the pedal down and clean deep in there. i had the same problem did that and all went away.
 

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2002 chevy trailblazer_lt_ext
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Discussion Starter #14
Update-

I did Seafoam...great clouds of smoke but no improvements in the way the TB runs. Previously did the air filter.

So the car went to the dealer today (again). It turns out the thing had been to the dealer service department several times, at a cost of $100 each time, for diagnosis of the stalling problem starting at about 18K miles. The CPAS had (finally) been changed at 51K miles. Now the dealer says the 'puter is throwing out the 0014 code. But I have little or no confidence in their diagnosis- primarily becasue they also said the engine mounts were bad (these were replaced less than 1K miles ago). They said the throttle body needed to be cleaned, which has been done three times since I started driving the vehicle. How can I trust a dealer service department that would return a vehicle to its owner in an unsafe condition, several times now, without being able to diagnose the problem?

Kudos too all here in TrailVoy...I've learned far more about potential fixes here than anywhere else. Pity the dealer service center doesn't seem to know about it, or perhaps they might have fixed it by now! Anyway, they're changing the CPAS. Charges are being disputed, primarily because the stalling issue goes back to well within the original warranty coverage and they've never fixed it. I also mentioned the fuel pressure regulator.

So could something like this be caused by a small crack in the intake manifold or some other kind of vacuum leak like that? Just spitballing.

Thanks again for all the help!
 

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2002 chevy trailblazer_lt_ext
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Discussion Starter #15
It's been a while, and we're still battling this issue. The TB's engine will shut itself off unpredictably at seemingly random times. The other day a family member was exiting the freeway at 50 MPH and the engine shut off. The driver was able to maintain control, and the engine was restarted after she brought the vehicle to a stop (without power brakes or steering of course- luckily there were no curves or other traffic in the immediate vicinity). The TB has stalled on me when I was coasting to a stop several times before. The same thing has happened to my wife- with my son in the car. We're now talking about a straight-up safety issue. The common denominator seems to be when the accelerator pedal has no pressure on it the engine "can" shut itself off- at any speed from stopped to 50 MPH. The dealership service department has essentially told us they're "in the dark" because the vehicle is not throwing service codes so they don't know how to diagnose it...even though over the years they've collected thousands of $$ in deductibles and after warranty fees for trying to fix it unsuccessfully. They try something and give it back to us, telling us to "try it for a week or two and see if it's better". They haven't personally been terrified by having to recover from a suddenly dead engine at 25, 35, or 50 MPH like we have. The engine will still nearly stall when stopped / idling if a slight pressure is put on the yes pedal. Sometimes it recovers, sometimes not. Does anybody have any ideas? We've already tried everything previously mentioned in this thread now. New CPAS, Seafoam, TB cleaning, TB replacement, fuel system flush...throw me a new idea PLEASE! Fuel pressure?

Thanks!
 
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