I just recently started having some random stumbling under light throttle (between -3psi to -7psi vacuum or so). As it gets closer to 0psi or is in boost, it goes away. It's more noticeable in the lower gears obviously, but I'm scratching my head as to what it can be. It even does it on the bone stock non-Trifecta GM flash.

It's been at the dealer to get a tranny seal fixed that they messed up, and had them look into it while it was there. So far they haven't found any vacuum/boost leaks (what I thought it might have been) and they think it may be a good reason to do a fuel system treatment to it. If it's a clogged fuel sock/"filter" or injector, I'd imagine that this would be more of an issue as you go up in throttle and fuel requirements go up.

Just throwing this out there to get educated opinions. Any ideas? Thanks.

I may try doing a boost leak test myself when I get it back, to see if anything comes up. I may check the plugs and O2 sensor too.

 

have you cleaned your throttle body lately?
my 08 with 48k just started hesitating and stumbling sometimes around 1600-1900 rpms when under light throttle and cruising.
just got it cleaned and its running better than it has in a while.

 

It's possible I guess. Thanks for the thought. I haven't inspected it in a while. I'll see what they say. If they want an arm and a leg or something, I'll check it out myself. I'm a bit burnt out on pulling things apart on the car right now after the doing the engine swap a earlier this year. lol

 

its worth a shot...i paid 25 to get it cleaned. its not as bad as people imagine if you have tools. i watched the guys do it and now know what to do when i get tools.
however i am fully aware the dealer would charge an arm and a leg...

 

Well I talked with them and it looks like they include it as a part of this fuel system service thing that they're pitching me. To their point, the injectors do have quite a bit of mileage on them, and I'm sure that switching back and forth between 93 and E85 during their life hasn't helped things. The treatment would be cheaper than new injectors. Perhaps it's worth a shot. hmm...

I'm going to go down to the dealer and drive it to give them a demo of what's going on.

 

The TB should not be cleaned with carb cleaner. It's an excellent way of ruining the TB sensor, and forcing you to buy a new TB. Just leave it alone.

 

How did everything come together for you yesterday with demonstrating the stumbling for your dealership? Thoughts on where you're going from here?
Sarah
GM Customer Service

 

My car does the same thing cruising about 25-30 Haven't really checked on it since it only does it a handful of times

 

Two people that drove it said they didn't feel it. Two that drove it said they did. I don't know how somebody wouldn't feel it unless they aren't following what I told them causes it.

They were thinking it could be the clutch (but a clutch doesn't do that, and it has never done that the whole time I've had it in there either), an aftermarket tune (but there is a bone stock tune on there), or something maybe with the fueling system (since they couldn't find a vacuum leak).

So they were left with doing a fuel system service and basically seeing if anything changed. They don't know what it could be. I've offered to go there and drive it for them with somebody in the car, and demonstrate it for them. My opinion is that it's either a vacuum/boost leak or perhaps an injector issue. I haven't really heard of these cars having much trouble with these direct injection injectors, so I'm leaning towards the intake system air leak possibilty.

 

It looks as though you are comfortable with your interactions with your dealerhsip; if I can be of any assistance, please don't hesitate to get in touch with me via private message (please include the last 8 digits of your VIN).

Best,
Sarah
GM Customer Service

 

I think Sarah's a bot. She has not ONCE posted pictures of herself. Either that or its one of those things like with Microsoft. You call customer support and its being done over in India.

 

It sounds like Cudajoe is calling you out Sarah!

 

 

Update:

-Did a boost leak test and found a couple leaks. Fixed those and the car was a bit happier. Tightened up all the clamps while I was there.
-Cleaned the air filter, and it helped a bit too.
-New O2 sensor and evap solenoid
-Pulled 3 of the sparkplugs and they don't seem out of the ordinary (the 4th is a bit of a pita and I didn't want to open myself up for another possible boost leak. lol)

Completely disabling the evap solenoid helps with the AFR swings, but the car still has a light stumble in vacuum. Idle seems just a tad off too. I got a P0130 (O2 sensor performance code) out of the blue recently when the O2 has less than 100 miles on it, I'm stumped there.

The only other things I can think of are a really small boost leak, a really small exhaust leak throwing off the O2 sensor, or a coilpack/injector issue. All the pistons look clean and shiny. Piston 1 had a couple drops of oil on it I saw, but nothing unusual. Guess I can go ahead and check cylinder 2.

 

My car does this too. Sometimes it's really bad, sometimes it's really light. I'm going to do a boost leak test like you suggested to see if I can find anything.
Please keep us posted!

 

I have a buddy with a turbo Seadoo in the shop for the same thing. I'll let you know if his mechanics come up with anything comparable.

 

Have any of y'all found anything?

 

I'm not trying to give an online diagnosis but as it happens. I had this EXACT same issue a while back. I replaced the stock bpv with a Forge one and all issues stopped.

 

Interesting...

Well, when you took out the stock diaphragm, did it appear damaged? If so, it may be worth me popping mine out and checking for any rips/damage.

Thanks for the idea.

 

My car does the same thing..it really hates when its cold as well..Its annoying and sometimes embarrassing when it happens lol

 

No. I didn't have any damage that could be seen. My theory is that the diaphragm can "rock" or... "tilt" on its axis. Which would be entirely possible if the pressure on it were near zero. There's plenty of slop between the center of the diaphragm and the guide. Leaving the spring to hold things steady. You can imagine if you had a weight sitting on top of a spring. It would be like a bobble-head. That's just about the best example I can come up with.
The only test really besides looking for damage is to swap with a car that doesn't have those symptoms.

I really noticed it while cruising say..... around 75-80 mph. The car would noticeably buck a little bit and I could hear it "psss, pss..pssssss" in quick succession. That was my biggest symptom but I did notice it in lower gears while accelerating lightly.

 

Binary solo.
0000001

Sarah, GM Customer Service

 

I see you're an old school 7-bit kinda girl. Living life without a checksum... a risk taker too I see! That's hott.

 

same thing that's happening to my '08 TC(stage2) right now, don't now what to do...gone to the dealership few times,change the fuel injector, sensors..they can't seem to pin point the problem..now it's worse, stalled me on second gear..doing this crazy sound like "Toooododododo",,scary..need help?

 

I'm not sure what you mean by Stage 2 for the SS/TC (there's no such thing... there was for the supercharged ones...), but there was a GM Stage 1 kit that included new sensors and a new tune. If you have that installed, the dealers would commonly mess up the rewiring for the new sensors, causing them to have a bad connection. People would get what you're describing or have the car go into a kind of limp mode.

If you've gotten the GM Stage 1 kit installed, I'd check the wiring going to the pressure sensors on the charge piping. Many people have had problems with the dealer doing a bad job on them.