My G6 is acting up again. This time when I'm driving anywhere from 30 to 60mph and I let the car coast it starts to goof up. It will drop in RPM slowly but will buck by 200rpm every couple seconds like it's stuttering. The slower I go the worse it gets, the rpms will bounce back and forth by 200 or so until I come to a stop. I've took it to my dealership four times now for this problem and they can't find anything wrong with it. They had it for three hours today hooked up to a computer trying to get a code read. I have no service lights and any computer it's hooked up to say's there's no problem. They said they can't do anything to it unless they get a code saying something's wrong. Anybody have a clue what could cause that?

Did they test drive the car themselves?

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05 Impala SS: INTENSE FWI - INTENSE 180* t-stat - Autolite 104 plugs

Yeah, they had it hooked up to two separate computers, test drove it several times, and rode with me while I showed them what was happening.

Well, the good news on this is that it isn't my tranny acting up. The bad news is I still can't figure out what it is and the dealership said unless it's throwing codes that they're not looking at it anymore. I recorded it messing up on my way home. This is how it acts when I coast to a stop. I did this in neutral, so that's what ruled out my tranny.
http://tinypic.com/player.php?v=2ld7nh3&s=5

You know the Drive By Wire throttle Body is electronically controlled... makes me wonder if your throttle body is going bad.. Its spring loaded to close and is actuated by the motor to open... seems like it may be having a hard time coming down to idle or the PCM is having issues with the Throttle plate position...

Either way there is an issue there someplace.. Should be pretty simple... If the PCM is calling for a certain position but is seeing something else then there is a problem that they should be able to diagnose...

I was wondering if the PCM was messing up. I had it updated before I went to Florida and that's when it started messing up. What else is weird is that it doesn't happen all the time. It takes some driving before it will mess up, like after a hour or so, and it only will do that when I slow down or coast.

Something is definitely wrong someplace as it should not do this.. And if you had them in the car with you driving while this was happening you'd think they would have looked deeper into the issue...