04 Cavalier Engine Vibration

I've owned my 2004 Cavalier for about 4 years now and I've had an issue with engine vibration for a while now. When ever I come to a stop and the RPM's drop to around 600-750 the dash board vibrates rather excessive, but stops once I'm idling around 500. Then if I accelerate slowly I feel it again but once it passes 750 it goes away. If I accelerate fast I don't notice any vibration at all. It gets worse if the A/C compressor is running. A couple of years ago I found I had a broken motor mount and got it replaced, it helped a little but the vibration never completely went away. I've had it stall out a handful of times when I'm at a red light and start to accelerate, but it hasn't done this in a while. Other than that the car runs great, just gets annoying after a while, especially during the summer months. I'm just wondering if anyone here has had a similar issue or would know what would be the cause.

You've got a second motor mount that could be bad, plus two transmission mounts.

What do the spark plugs look like? Pull the cover off the throttle body and look inside. If the carbon looks like it's piled up, have an induction flush done on it. I prefer BG myself. Pull the IAC valve off and clean it out too.

Mine does the exact same thing, but only on coastdown. On mine, it feels like the IAC closes completely and then opens too late which makes the engine struggle to go again. I reprogrammed my PCM, so it's possible that is what's causing the shudder. I also have all new polyurethane engine/trans mounts, so I can rule that out on mine. I don't personally care enough to look for it, but if I stumble on the cause I'll let you know.