I have a 97 Kia Sportage and I've had the same probelms that you've had.
Take it to a Auto place that has a computer that could tell you what to look for in fixing it.
Like at AutoZone or something.
The test is free.
OKay, the same exact probelm has happened to mine, so far this is what I've done to mine.
I've replaced both coil packs , cause I was told one was bad, though still the same problem.
Then I changed the spark plug , which was firing arm number 4 that wasn't doing well.
Then I changed the water pump, still to no avail, it's still messed up.
I'm taking mine back to the dealership Monday and I'll keep you posted.
The next idea from here would be look into your fuel line , or then look into the ERG Valve.
ps. my kia is a 97 model.