Hyundai Repair: 2001 Elantra misfire/erratic idle, elantra gt, obd ii code

Question
I have a 2001 Elantra GT with 92k miles. My problems began with rough idle. Soon afterwards, check engine light came on. I replaced the plugs with Autolite Platinums. Check engine returned and problem progressed to erratic idle (up to 3500rpm). Obd II Code was 303 (misfire). I changed to new plug wires and moved cyl 3 plug to cyl 1 with hopes to eliminate the chance of a bad plug. After that, I got 303 and 507 (high idle) codes. I measured resistance across primary and secondary coil windings. Both were about the same (0.6-0.7 ohm & 14-15 kohm). Are the coils to blame or am I chasing the wrong system? Thanks in advance.

Answer
If the yave poor performace off idle, you should continue investigating the ignition system.  To check, remove the number three wire from the plug and install a known good plug in the end of the wire.  Lay the plug on a metal portion of the engine (keep away from fuel and flammables)such as the plenum and start the car.  If the plug sparks, you should expect the ignition is okay.  If not, your problem lies somewhere within the ignition system.

If the problem only occurs at idle, check for an intake manifold leak around cylinder number three.  That would be consistent with the single cylinder misfire code and the idle issue.