Like already stated: I would do the "key Dance" first

1. Have a pencil and paper handy.
2. Get in the car, close the door.

Perform steps 3-7 fairly quickly (less than 3 sec's total time).

3. Turn key to 'ON' position
4. then back to 'OFF'
5. then to 'ON'
6. then back to 'OFF'
7. then to 'ON'

If there are any stored codes, they will appear immediately, in place of the odometer.

Once the codes have been displayed, you'll see "-----". If there are no trouble codes, the dashes will be the first item displayed.
After a few seconds, the display changes to "-dOnE-".

 

Any codes yet, key dance !

 

Because the ignition switch is different on the 2008's and up, the "key dance" is also slightly different. While it will work going all the way back to OFF, it isn't necessary, it's much easier to just cycle between ACC and ON.

So steps 3 thru 7 could read:

3. Turn key to 'ON' position
4. then back to 'ACC'
5. then to 'ON'
6. then back to 'ACC'
7. then to 'ON'

 

That's a new one on the key dance Georgef, good to know.

 

My 2002 GV is: ACC-OFF-ON-START if I remember correctly

I remember because I had the usual problem when I just got my GV with battery drains, leaving the car in "ACC" every time I left the vehicle

 

I never knew you could do that! Very cool. Nice to not have to run to my mechanic every time to check for codes. Is there a way to erase codes in a similar way as well?

 

As far as I know you erase all codes by disconnecting the battery for 30 minutes.
After that you drive around the block and check codes again, those that pop up again need attention

 

You can clear the codes in 10 seconds by removing ONE battery wire and touch it to the other one for 10 seconds. this kills all of capacitors in everything and start new. I feel i must mention DO NOT SHORT across the battery.

I do this all the time.

Mr. Fixit

 

Well, I can bank the info on clearing codes for next time 'cause I got no codes thrown when I used the technique. So, we have a suggestion of possible temp sensor, a buddy who mentioned it may be a spark plug or plug coil starting to go. Any other ideas and more importantly, what should I do next? How do you test a temp sensor? Would it have thrown a code if it were a sensor? Same question about the possible plug or coil issue. Thanks for any advice on how to procede from here. Still bucking when holding at constant, steady speed and had a stall 3 days ago (outside temp was about 45 degrees but not sure if temp related issue yet as we haven't warmed up enough in Boston to differentiate).

 

I think you should do a full service first;
Air filter, fuel filter, oil & filter, spark plugs. If this has helped but still not 100% then replace the coil packs. At least you now know you have a good base to start from with further fault finding and knowledge that your engine should be in a better state of health.