Kia Injection Idle Problems

Hi, I have a Kia Sephia 98 with 86,000 miles. Last I took it to a mechanic they changed the injection electrical sensor. It was idling all over and sometimes spitting black smoke out the exhaust. The check engine light was on, but after they changed the sensor it went off.

Since then the gas millage is much worse.

Now three weeks later its idling weird again... Its almost dropping off, a couple times it stalls at a stop in drive. Sometimes at a red light I put it in neutral but it will either rev up to 2000 rpms or almost drop off.

Its like its speratically injecting gas, I have horrible gas millage like 10 miles to the gallon. While driving at a constant speed it will suddenly jolt like its injecting extra gas and then going back to normal.

I took it to a mechanic and they didn't even want to look at it... So I need to find another mechanic. But if anyone has any advice on where the problem is, how I should approach a mechanic. I am a mom and need this car to get me through the next few months.

Oh and when I turn the car cold fluid, like AC condensation is puring onto the floor from under the glove box????? Any idea on what that is?