For the past couple of days I have stumbled upon an unsettling problem. I stop at a stoplight and while the care is still in drive my vehicle shakes for about 1 second, then is okay, then shakes for 1 second, then is okay for a second, until I begin to move again. I am thinking it may be the alternator, since when it shakes and gets loud the entire cosole gets a little dimmer, but I'm not sure if it is something else. The wierd thing is it doesn't happen all the time and seems to be when I'm coming home from work at 7AM, when it is still hot out, but not too hot. It has been a heat index of about 107 for the past week or so in Chicago. I'm just hoping someone has had the same problem, so I can be pointed in the right direction. This is the first thing that has gone wrong with my TL, and for a minute I was unsure if I would be able to get it home, even though it's 1 mile from where it happened. If anyone has any ideas please post them...I could use any type of ideas.

 

Is your ac on? its probably the ac compresor cycling on and off, which will cause a rougher idle. Along with that you may have some worn out motor mounts adding to it

 

You might check the battery connection if is tight ...
when lights get dimmer it could be your alternator
or your battery .....