1998 Chevy S-10 Engine runs poorly except when A/C is runni

For the past few months, my S-10 has been running very poorly. When driving at speed, the engine sputters like there is water in the gas. At stop lights or stop signs, the engine idles very low and at times will not accelerate out of the stop. The service engine light on the truck would regularly come on and then cycle out when the truck was turned off. It usually took about 20-30 miles for it to pop back up again.

Here's where it gets really interesting for me. My A/C has not been running on the truck for quite a while due to an assumption I made (based on bad advice) that there was a major problem with the system. I decided a couple of weeks ago to try charging the system and it worked! Now I have wonderfully refreshing air!

The greatest result is I have found that when the A/C is running, the engine runs very smoothly with none of the issues I mentioned. It doesn't sputter at speed, die at stops, and the service engine light has not come on once. Can you give me some idea as to what could be causing the problem? I have been told it might be a problem with the A/C sensor, but have never even heard of it. Thanks for the help!