1992 Integra GS idling too low

I've been having this problem for as long as I can remember. My car idles very roughly when I am stationary at a stop sign or stop light. Even after the car is warm, shut off, and then started up again, the initial turning on of the car brings the RPM's down to around 600.I know the idle RPM range is 700 +/- 50 RPM on this car, but it just doesn't feel right even when it happens to reach those RPM's at idle.I've turned the idle speed up to help alleviate the low idle, but even that didn't help. The car goes right back down to 600 RPM's at times, and it fluctuates a lot. Not by much, maybe 50 RPM's. And when it fluctuates, I can hear my exhaust making a gurgling sound, almost like a mini back fire. It isn't a smooth sound.I appreciate any help. Thanks