Stumbling/Missing at light throttle input......mostly cruise control

gladesteen

Original poster
Member
Aug 19, 2014
83
Over the past 2 weeks, my 2004 Bravada w/200k miles has been acting up. It seems to only do this after at least 30 mins of driving. What i'm feeling is a hard stumble, that feels exactly like a misfire (have been thru this before) but i'm not seeing ANY CODES. Nothing. Not even a flash. It mostly happens during cruise control or very light throttle inputs. If i give it more throttle, it immediately goes away.

I pulled the throttle body off today and thoroughly cleaned it out. Wasnt even that bad. I did the trans filter/and 6 qts fluid this past May.

Any suggestions would be greatly appreciated.

Thx,
Mark
 

Mooseman

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Dec 4, 2011
25,260
Ottawa, ON
Did you disconnect the battery or pull the PCM fuses while cleaning it, min. 30 minutes?
 
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mrrsm

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A Clogged CPAS along with infrequent Oil and Oil Filter Changes happening religiously at 3,000 Miles using ONLY Fully Synthetic Motor Oil and HQ Oil Filters on Very High Mileage Engines... it can emulate problems similar to having P03XX Mis-Fire Codes and yet... still NOT throw any Codes.

This of course assumes that you don't already have High Mis-Fire Counts collecting in the PCM RAM that point to one or more cylinders having either Tired Spark Plug(s), Shorting-Failing COP(s), or Dirty, Clogged EFI problems. A Sketchy Fuel Pump can also cause such stumbling.

If you have not recently pulled and cleaned the CPAS or if you can see Motor Oil coming from around the CPAS and leaving an Oil Slick Trail down the Passenger side of the Engine Block and/or presently infiltrating the CPAS Electrical Connector... Add these locations to your "Check These Symptoms" List.
 

gladesteen

Original poster
Member
Aug 19, 2014
83
A Clogged CPAS along with infrequent Oil and Oil Filter Changes happening religiously at 3,000 Miles using ONLY Fully Synthetic Motor Oil and HQ Oil Filters on Very High Mileage Engines... it can emulate problems similar to having P03XX Mis-Fire Codes and yet... still NOT throw any Codes.

This of course assumes that you don't already have High Mis-Fire Counts collecting in the PCM RAM that point to one or more cylinders having either Tired Spark Plug(s), Shorting-Failing COP(s), or Dirty, Clogged EFI problems. A Sketchy Fuel Pump can also cause such stumbling.

If you have not recently pulled and cleaned the CPAS or if you can see Motor Oil coming from around the CPAS and leaving an Oil Slick Trail down the Passenger side of the Engine Block and/or presently infiltrating the CPAS Electrical Connector... Add these locations to your "Check These Symptoms" List.


Thanks for the Inputs. I'm going to change the CPAS as i've never swapped it out before. Seems pretty easy to do. Just under the front left corner of pass valve cover. I did inspect things when i cleaned the throttle body and noticed the barrel of the VVT spins. There was nothing "wet" but saw some darker discoloration near the electrical connection.

I recently (year ago) changed plugs with iridiums and put new coil packs in as well. So i'm pretty sure all is well there. Additionally, i only use Mobil1 5w-30 High Mileage Fully Synthetic every 3k miles too.
 
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gladesteen

Original poster
Member
Aug 19, 2014
83
Just a follow-up....today i pulled the CPAS and cleaned it up, put back in. Upon looking at Amazon, i DID purchase and change the CPAS in 2017.

After doing that, i took it for another test drive. Still the same thing. Definitely happens more on cruise control highway speeds, but can also duplicate at 40mph with light throttle inputs. Feels exactly like a failing coil pack, but zero codes and nothing pending either.

Any other ideas? Should i just order a new CPAS and VVT ?
 

Mooseman

Moderator
Dec 4, 2011
25,260
Ottawa, ON
What brand plugs did you use? This engine is very sensitive to plugs. We strongly recommend only ACDelco 41-103.
 

seanpooh

Member
Jan 24, 2012
461
Any chance you can get your hands on a scan tool that monitor misfires for each cylinder? That would help a lot. Again, that's only if it is indeed a misfire going on.

Does your RPM flutter while you're cruising when the "hard stumble" is happening?
 

gladesteen

Original poster
Member
Aug 19, 2014
83
What brand plugs did you use? This engine is very sensitive to plugs. We strongly recommend only ACDelco 41-103.
Yes Moose, i use only them -- they're also known as Iridiums
"I recently (year ago) changed plugs with iridiums and put new coil packs in as well. "
 

gladesteen

Original poster
Member
Aug 19, 2014
83
Any chance you can get your hands on a scan tool that monitor misfires for each cylinder? That would help a lot. Again, that's only if it is indeed a misfire going on.

Does your RPM flutter while you're cruising when the "hard stumble" is happening?

Sean, I do have an active scanner (Torque) and will set that up. Been researching this quite a bit and i'm going to try a Seafoam treatment to clear some carbon out. Have just over 200k miles and have never done it, so it will surely be smoky. Heavy carbon buildup on the valves could be causing this also. I'm currently getting 15.8 mpg combined, so the Seafoam may help that

As for looking at the RPM's, my tach is currently down due to a bad stepper motor. I can see the tach using my Torque App tho, so i will look for that. I hope to NOT see the tach rise/flutter as that would point to tranny issues.
 

Mooseman

Moderator
Dec 4, 2011
25,260
Ottawa, ON
Yes Moose, i use only them -- they're also known as Iridiums
"I recently (year ago) changed plugs with iridiums and put new coil packs in as well. "

OK. just making sure :biggrin: . Where did you get them? There has been a proliferation of fake ACDelco plugs lately. What about the coils? Were they cheap no-name or off-brand?

Can you check for misfires using Torque? It might be misfiring but not enough to trigger a code. Fuel trims might also be useful as well as MAP data.
 

gladesteen

Original poster
Member
Aug 19, 2014
83
OK. just making sure :biggrin: . Where did you get them? There has been a proliferation of fake ACDelco plugs lately. What about the coils? Were they cheap no-name or off-brand?

Can you check for misfires using Torque? It might be misfiring but not enough to trigger a code. Fuel trims might also be useful as well as MAP data.

Got the plugs and coils from Amazon. The plugs were definitely AC Delco and not knockoffs. I had one of my original AC Delco/Delphi coil packs fail, thats why i swapped them all out. ( I actually saved the other 5 factory ones). The coil packs i bought were knockoffs, but highly rated. Here's the ones i bought.

https://www.amazon.com/dp/B00M07GQO0/?tag=gmtnation-20

I installed the plugs and coil packs 2 years ago. They've been perfect so far. When i had the original coil pack fail, it was easy to diagnose, threw the right code and was completely undriveable.
This issue ONLY happens during cruise control at highway speeds or very slight throttle inputs after 30 mins or more of driving. Never happens at all when cold.

As for the Torque App diagnosing misfires, it seems it can do this. I found a helpful YouTube video to help me out.
 
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gladesteen

Original poster
Member
Aug 19, 2014
83
Update:

Its the transmission. More than likely the Torque Converter or Valve issues. I had the pan/filter/fluid changed right before xmas and everything was PERFECT for 2 weeks. Then yesterday, at around 45 mph with light throttle, i'm getting a severe shudder. Feels like i'm rolling over cattle grates. Looks like i need to take it to a transmission shop. This may be the end of the Bravada for me. I cant keep throwing money at her....considering book value is $1000....hahaa
 
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