Rough idle at stoplights and somewhat in park.

[Scholzpdx]

Hello everyone!

I've got a 99 SL1 161K Auto, and recently every once in a while (1 out of 5-7 drives) the car seems like it's chugging along at stoplights. The idle sounds and feels rough. This happens once it gets warm, usually. The rpms barely bounce at 650-700 when in D, but you can feel it in the cabin. I just got my upper mount replaced (GM mount, $100) and I thought that would fix it. It just sounds about 100x better because the engine isn't rocking now, but you can still noticeably feel it. When I put it in park I could kind of feel it there as well.

No SES light, no codes, nothing. But something is amiss. It doesn't sound like it's running right in neutral with the hood up.

Does this sound like a timing chain? Spark plugs? EGR? I'm lost on how to tackle this. And relatively broke. I'm on workers comp from a work injury.

Thanks in advance.