Hi everyone I have a 2005 bonneville sle with 110k miles on it....I am getting a slight misfire or stumble this only happens when the torque converter is fully locked up in 3rd or 4th gear and I'm am lightly accelerating to not allow a downshift or big rpm change....at first I thought it was the tcc solenoid I took it to a tranny shop and they said it is not the problem..and it is a very mild misfire...I am getting no codes...I have recenlty changed plugs, wires, brake switch and fuel filter and made no difference...any help would be appreciated from anyone who has experienced this, before I start changing parts that could cause this...coil packs,injectors,fuel pressure regulator,egr, etc. Car runs perfect and no problems in other gears and very strong through whole rpm range....only the o.d. stumble

Thanks,
Anthony

Take a look at this write up and see if it helps. https://www.gmforum.com/electrical-133/tcc-solenoid-switch-284972/

I did the simple test that was in the write up and it is working....the rpms jumped when I pressed the brakes and then returned....does this mean it is ok?....I am still going to test the switch tho and see what happens

Okay so I tested the tcc switch and it is functioning properly....strange thing today tho...now the car is idling rough at startup then kinda clears up after about 30 seconds but still a bit rough after...and is now hesitating at takeoff until about 3k rpms....I also noticed a lot of what seems like white ash specks at the end of both exhaust pipes...still no codes what could be going on?

Plugged catalytic converter.

Damn that'* not good if it is that...it was just replaced about 40 thousand miles ago under federal emissions warranty at gm....I remembered I asked the tech to find out what was the leading cause to make it go bad and he told me they could find nothing wrong and it just went out

Mine went out on my Camaro at around 72k. They said it was the type of gas I was using. Changed to higher quality fuel and didn't have problems since.

Since day one when I bought it I have been putting midgrade chevron never anything else....so would u know what the white specks would be on the end of the pipes

Hmmm, that'* good gas. I'm guessing the white specks would be pieces of carbon or something coming from the exhaust system somewhere.

I kinda wonder if you are experiencing detonation or knock retard.