Feeling blue? need to vent? need an opinion? Lets talk about it
I have a 2008 Nissan Sentra with about 115,000 miles on it. It has been tuned up recently and it is current on all scheduled maintenance. I have recently noticed that when:

1) The air conditioner is on, and
2) I have it in drive or reverse, with
3) my foot on the brake.

The RPM will dip periodically from 750 (which I assume is normal) to 500 to 600. When this happens it feels like the engine is going to die for a second then it quicky jumps back up to 750. You can tell that something isn’t right, however, it has never stalled. I have never noticed this with the air conditioner off.

I had the air conditioner serviced when I first noticed it and it was a little low on coolant. It has been filled to capacity now and this RPM dip still happens. I’ve noticed no change in frequency.

I need to stress that this is very intermittent. Sometimes it happens a lot and with other trips it idles normally with my foot on the brake.

Also, I should stress that the RPM only dips down, it doesn’t surge upward. I have done some internet research and there is a lot of talk about Sentras having a problem with RPM surging upward while in idle, or both up and down, and I’m certain that is not the same behavior I’m dealing with.

Please let me know if you have any ideas. This is starting to get frustrating. I've owned 3 Sentras, drove one to nearly 400,000 miles, and I have never had a problem like this.
raise your idle slightly
some idle fluctuation is to be expected with additional load

try 800-850 rpm idle

use an after mkt app
tq pro or such with a dongle to change idle speed
expensive to take to nissan, but that will work

check the factory shop manual [fsm] for the correct idle speed
available on site
yours sounds a bit low

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