Denny...
I don't know but I would think the plugs you used were either "Special" design (like the BOSCH multi electrode) or were gapped incorrectly...
Many plugs come "pre-gapped" for 90% of the cars they were made for..The other 10% will end up with the wrong gap and problems...
From NGKs website...
"Gapping
Since the gap size has a direct affect on the spark plug's tip temperature
and on the voltage necessary to ionize (light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the vehicle that the spark plug is intended for."
Spark Plug Installation Instructions
Always check the gap of EVERY plug you install... I like and use NGKs in my 2.0L Spectra ...BUT... I always check the preset gaps before installing them... Even NGK has been way off on a few of their plugs and they required adjustment...
Your RIO (as well as our Spectras) needs their plugs gapped to .044"
Both my wife's and my Spectra came with "Champion" brand plugs from the factory... I believe there was a commercial campaign agreement between KIA and Champion...
My wifes Spectra at 60k miles was misfiring just after replacing the timing belt..
I pulled the plugs and found the center electrode ceramic insulator on one of the plugs had cracked up inside and then fell down over the center electrode..effectively insulating the spark from the air/fuel mix... I replaced the plugs on both cars with NGK
platinums...
KIA's engines have gone through a few revisions and they were designed to use NGK or Denso brand single electrode plugs.. Plugs like the BOSCH cause mis-fires, and poor performance...Proven HERE by posters...
Platinum plugs work fine in KIAs as well as Iridium and Copper, The difference is the amount of miles you can go before the electrodes wear down and you need to replace them...
Copper around 30k miles
Platinum around 60~100k miles (I'd replace them at 60k)
Iridium around 100~120k miles
I would really like to know the brand and part# of the set of plugs you are giving away..Not so much as because I want them as to understand "why" they ran so poorly..
If you have arching ANYWHERE in high voltage wiring you have problems...
That's why they have rubber boots and HV wires... A cold car often has condensation on it's parts and HV and moisture are a bad mix.. I'd suggest replacing the rubber boot and/or the coil itself... As the car warms up the moisture "boils off" and the misfire goes away till the next morning... Silicon spray is a "temp-fix" ...Solve the problem..
As far as getting to the plugs...a well designed spark plug socket (SEARS) and a long 3/8" extension will solve that problem...
Dave