hesitation and stumbling [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: hesitation and stumbling

08-23-2010, 12:59 PM
Hi, This issue has been discussed several times on various posts, with no real fix posted. Anyway my 2002 trailblazer has developed about 5 weeks ago a hesitation/stumbling issue, sometimes it will stall. The issue was intermittent but now happens almost all the time. The condition happens with a cold start or has been sitting a few hours. I start the TB and drive away, with in a few seconds or can take up to a minute or two it starts it's hesitation and stumbling. I have never had it stall or stumble while sitting in the driveway warming up. The issue will go away if I restart the TB or just let it do it's thing then it starts to run fine. Once warmed up it runs perfect. I have 98000miles (158000kms) I am in Canada. I changed the plugs back in November using the Delco iridium's, new air filter,new fuel filter, completely removed the throttlebody and cleaned it so it shines front and back. Also ran some fuel injector cleaner through it, Tried some gasline anti freeze to remove any water, even tried a different brand of gas. it's been on the tech II twice in a month with no trouble codes or miss fire history. O2 sensors are with in parameters. I have read of a PCM firmware up date or doing something with the evap solenoid. the stealership wants $83 to flash the PCM plus labor with what he said was the latest and greatest update they can find for my year TB.
Any help with what others did to solve this seemingly growing issue for good before I keep throwing more money aimlessly at it.

08-23-2010, 05:16 PM
my 05 has simaler issues found a bad cam sensor.
have you scanned it?

08-24-2010, 01:12 PM
Yes All sensors were scanned with the tech II . The TB runs great once it gets past the hesitation/stumbling issue. When I removed the throttlebody and cleaned it all out (yes I disconnected the battery) The TB had better response and a nice smooth idle. This service did nothing to fix my issue though.
Hopefully someone with this problem will write in as to what fixed there similar issue. Thanks for the cam sensor suggestion, hopefully more will write.

08-24-2010, 03:16 PM
I had the same exact problem. TB was running like garbage. Stalling, failing, missing, everything you could think. I replaced the crank shaft and cam shaft sensors (by advice from my dad) and it runs like a champ! I would imagine I had been driving around on six cylinders for a while. Also, clean the throttle body from this post and that will help alot. It made a world of difference for really not that much work.


08-24-2010, 04:38 PM
I had this problem and it was the butterfly valve. It is underneath the resonator box. You have to disconnect your battery before you mess with it though because you can mess up the servos if you don't. When it's cold the carbon build-up can be very sticky and create a little ledge thus not letting it open right to allow enough air into the mixture before it enters the cylinders. It becomes less sticky as the carbon/petroleum buildup heats and becomes less viscus and the atoms don't stick together as easily. You can remove the whole valve assembly to clean it with brake cleaner and a cloth but be careful because the edges are sharp and can slice you up quickly.

08-24-2010, 05:47 PM
I would imagine I had been driving around on six cylinders for a while.


I would hope you were running on 6 cylinders, your profile states thats what you drive

08-25-2010, 12:04 AM
You will be safer if you use a cleaner that states it is throttle body safe. :m2:

08-25-2010, 01:59 PM
Ok I took the Trailblazer to the dealer, talked to the shopforman there. I explained to him all that has gone on and what I have done to the TB. He checked it again with the techII. Nothing. Said he has seen this issue before on these trucks. Looks at the cam position actuator valve. Its wet with oil, Unplugs it and the inner electrical pins are wet with oil internally. He suggests starting with replacing the cam position valve as this will cause my condition.
I bought a replacement sensor and left to do the job myself.

Question, how do you remove the sensor? I pulled the 10 mm bolt and pulled it out as far as I can. The valve is about 6 inches long, comes out of the head . The power steering pump reservoir is in the way for complete removal.
Has anyone done this repair before? Do I need to remove the power steering pump assembly or is there a trick to this !

Any help appreciated...

08-26-2010, 12:10 AM
The serpentine belt needs to be removed and the pump has to be moved out of the way. :m2:

08-26-2010, 01:24 PM
Thanks WOOLUF1952. I figured it out and removed the belt and loosened all three power steering 13mm bolts from the pump. Pushed the pump back towards the firewall a few inches. It gave me enough room to get the cam position actuator solenoid valve out. The old one internally was in great condition. It was really clean, no debris in the tiny screens. All three screens in place and in perfect condition. I did read that some people have had the screens missing or loose !! My solenoid was leaking oil past the internal seal and filled the electrical end with oil.
Took maybe 45 minutes total to do the job, I disconnected the battery too (not sure if needed but played safe) I took the TB out for a drive (cold start) and my problem seems to have been fixed. I will post back if my hesitation/stumble issue returns. Thanks to all the members who took the time to respond to my post. Hopefully the info here helps others.

09-03-2010, 05:33 PM
The new cam actuator didn't solve my cold start hesitation/stumbling issue. Again once the Trailblazer gets over it's hesitation or is warmed up it runs like new, lots of power, perfect idle . If anyone has any input on what other sensor could cause this condition let me know. The issue is driving me nut's and I am in no position to keep throwing money at it aimlessly. Anyone know if a crank sensor would cause this condition? Would a bad crank sensor be a issue all the time. There are no trouble codes either. Stumped:bonk:

09-05-2010, 10:29 PM
Hey, mine is doing the same. I cleaned the TB but nothing. It only happens in the morning or when I first start up the SUV. After I restart the car, it usually runs fine during the whole day.

09-05-2010, 10:46 PM
If you've cleaned your throttle body, your cam solenoid is ok and you are still having the problem, what code is coming up with your check engine light (if you are getting a code, that is). If there is no code, check all vacuum lines for dry rot/cracking. Your problems seems to be a bit of a mystery after reading the posts.

As a sidebar, all an engine needs to run is gas, air, and spark.

Does your air filer need changed? (there is a gauge built into the intake)
Have you changed your plugs or is there any code for a failed coil pack?
Is your fuel filter clogged?

Just some simple thoughts about your stalling. As another sidebar, I had a problem in an older vehicle that would cause it to stall when I made a right hand turn, ended up the fuel line became pinched when I cut the wheels... :(

09-06-2010, 09:32 AM
Thanks for your input, will have to check the fuel filter. Only problem is, my TB isn't running any bad codes. Makes it very hard to tell. It runs like a champ after the second start up.

09-06-2010, 10:23 AM
Ok this is what has been done to the trailblazer. New acdelco iridium plugs ( did them last fall, only plugs at that time) , new fram airfilter, new fuel filter , cleaned the throttlebody twice in 8 months since plug change , yes a full removal clean, front and back. new cam position actuator solenoid. There are no trouble codes , I have ran injector cleaner through it. Ran gas line anti freeze to remove any water in the fuel. even changed brands of gas with no change at all. The truck like the other poster jordanball28 only has the hesitation issue when started in the morning, great running the rest of the day. I will check vac lines, I have looked at them briefly and all looks good. One other member on another post mentioned battery condition. Would a older battery cause this cold start/cold running condition? Not sure of the battery's history or age. It started the trailblazer all last winter while outside without issue. My poor cold start condition started about 7 weeks ago. It was intermittent but now is happening every cold start. It never does it again if I drive say a few hours later the same day. Dry or wet days is no different either. Keep the tips coming in on my mystery !

09-06-2010, 02:05 PM
Might be the camshaft sensor. Not sure though. I am just trying to read around the internet to figure out what this could be. I read somewhere saying that it wasn't the battery.

09-08-2010, 04:01 AM
Mine studders at every red light when I give it gas I deliver pizza in it. New spark plugs filter fuel filter full syn oil run lucus fuel injector cleaner in it

09-08-2010, 08:26 AM
The more i read, i feel like it is the cam shaft sensor. There is threads on how to replace it. Most of the time, oil will get build up in there. Try reading about it. I think it will solve your problem.

09-08-2010, 03:44 PM
Thanks for the tip jordanball28. I will do a little research on the cam sensor, I will post back later. I suspect it is a sensor. The issue started out of the blue, was intermittent for awhile. Now the truck runs like crap after it's first daily start for the first few minutes. It does it ever time now. I will check out cam sensors.

09-09-2010, 11:22 AM
I am about to take mine to get a diagnostic done to it, to really figure out the problem.

12-03-2010, 02:45 PM
Any update on whether the cam sensor was the problem? I'm having the same issue, stalling and rough idle at stop lights, no check engine light or codes. I had read in a different forum that someone with this problem found out that their O2 sensor was sending information too slowly, it didn't send a code or trigger the check engine light, but ended up being the culprit.

Has anyone looked into it and if so what was the result?

12-03-2010, 02:51 PM
I would hope you were running on 6 cylinders, your profile states thats what you drive

Yes... my mistake... I have a 6 cylinder! haha!

Anyways... Trailblazer runs like a champ now. Better fuel economy also. I dont know if the exact from the was the cam shaft positioning sensor or the crank shaft one or the throttle body being cleaned. But, that combo did it for me. Parts were very cheap and only took a couple hours in my garage with normal tools.

12-03-2010, 03:12 PM
I used to have a stumble and near stall back when the truck was new, when I complained, the dealer offered there was PCM update that fixed a cold surge/stumble condition. I'd been in there 3-4 times for various things and they never bother to mention it or do it! The '02 models can suffer from a surge/stumble when first started. Mine would last maybe the first block or two, when you'd attempt to apply throttle to pull from a stop. Much below 30 or over 70, problem was really non-existant or at least a non-issue. If that sounds like your issue, it could very well be you need that update.