Off idle stumble problem

[fastazz40th]

I`m stopped in drive or reverse and press the gas pedal and stumbles for one second. Then goes.

Once in drive, stopped, hit the gas and died. Had to restart it.

No check eng codes or anything in history.

[Gabe25]

Need to know more information.
Motor size.
Year.
Make.
Model.
Vin Number.

[fastazz40th]

Yeah, that would prolly b important. Sorry.
02 Bravada
4.2l 6 cyl
vin# 1ghdt13s422389576

[karlmarx]

So this happens as soon as you step on the gas? I have the same problem, but only when the car shifts between 1st and 2nd gear, a noticeable stumble and jolt.
We took the car ('02 Bravada) in to the shop today and they put it through some tests. The computer showed no errors and no history of errors. They did find a bulletin that says (and I'm quoting):

"The condition can be perceived as an engine misfire, surge or bump typically during or just after the 1-2 upshift. This condition can occur on Bravadas, 9-7X's and Rainiers NP4 with full time AWD. This will only happen in Trailblazers, Envoys NP8 when AWD (auto mode) is seleced. When Viewed through the TECH II, misfire counts may be occurring but not enough to set a misfire DTC. The concern will be eliminated in Bravadas and Rainiers with the ATC fuse removed or in Trailblazers and Envoys when in 2hi or 4hi is selected. "

From the "Recommendation/Instructions" section of the bulletin we get:

"This is likely a characteristic of the vehicle and some degree of this condition should be expected on all these vehicles. Comparing this vehicle to an identical vehicle with similar mileage should verify this is a design characteristic."

They then recommend some things to try: swapping tires, draining transfer case fluid and refill.

Basically: this is an inherent design problem in the full range of GM trucks/SUVs in this platform. Not sure why it would start now though. Ours only has 46k miles so pretty low.

So, the mystery continues...

Rob

[Gabe25]

Originally Posted by fastazz40th

I`m stopped in drive or reverse and press the gas pedal and stumbles for one second. Then goes.

Once in drive, stopped, hit the gas and died. Had to restart it.

No check eng codes or anything in history.

OK just a quick thought. Did you try removing your EGR valve and check for carbon chunks. You need to ensure that the Pindle moves freely without any restrictions. It should be in the close position when you remove it.
When re-installing the EGR valve. Make sure that you install a new gasket. Most prefer the one with a screen that keeps the chunks from resticting the pindle. Post back what you find.

[Gabe25]

Forgot. one more thing. How many miles do you have on your Truck?

[fastazz40th]

Thanks Rob for the reply. But there isn`t a problem with it on the 1-2 shift. It`s right off idle as soon as you press the go pedal and hesitates for a second in forward and reverse. Doesn`t do it all of the time though. Maybe 3 out of 5 times. Enough to be noticable.

Gabe: I will try cleaning the pintel. A screen is a good idea.
Although my experince with those are erratic idle in gear.

[Gabe25]

Originally Posted by fastazz40th

Thanks Rob for the reply. But there isn`t a problem with it on the 1-2 shift. It`s right off idle as soon as you press the go pedal and hesitates for a second in forward and reverse. Doesn`t do it all of the time though. Maybe 3 out of 5 times. Enough to be noticable.

Gabe: I will try cleaning the pintel. A screen is a good idea.
Although my experince with those are erratic idle in gear.

When was the last time you had a tune-up? Plugs, Cap, Rotor, Wire set. Here is a few other things you mite to check. Distributor Rotor Shaft. Make sure its not shifting around, Fuel pressure, Idle Air Controler,

[b1lk1]

My truck did something like this when the MAF was dirty.

[fastazz40th]

I asked the shop we took it to, to look at the maf. And they said it didn`t have one. I didn`t think that was right. They also told me it had a map sensor. Which i thought was the same thing as speed density. We have since taken it to another shop and they told us that there was a GM bulletin regaurding this stumble and the pcm needed to be reflashed with this update.

We get it back here any minute and we`ll see if that fixes it.

[fastazz40th]

The pcm reflash with new update fixed it.

Thanks for your help guys.

[Gabe25]

Originally Posted by fastazz40th

The pcm reflash with new update fixed it.

Thanks for your help guys.

Glad to hear everything is up and running. Have a great weekend.