“Bought the van in Aug of 10, had about 135,000 miles then and have put 12,000 miles on since. No clue when of if the plugs were ever changed.”
Hmmmm…Don’t ask, don’t tell–car maintenance version?
As we frequently advise on this board, if you make the mistake of buying a used car that did not come with full maintenance records, you have to assume that NONE of the prescribed maintenance has ever been done. In the case of your vehicle, if the previous owner knew that he was going to get rid of it in the next year or so, he may have gambled with ignoring the very major 90k mile service–knowing that the next owner would be more likely to suffer the consequences of lax maintenance than he was.
So–you need to take out the Owner’s Manual (You DO have one, I hope), and turn to the section for the Kia Maintenance Schedule. Make a list of everything that is listed for the 90k mile service, and have that done. The list will likely include changing all fluids, all filters, and the spark plugs. You would be wise to add a transmission fluid change to the list if it is not listed by the mfr. There is a very good chance that just bringing the vehicle up to date with necessary maintenance will resolve the misfire problem.
Also, take a look to see when the timing belt is supposed to be replaced on this engine. Most likely it was supposed to have been replaced at 105k miles or 7 years, whichever came first. In this case, in the absence of maintenance records, you also have to assume that this vital service has never been done, simply because when that timing belt snaps (not IF is snaps) your engine will become a steaming mass of damaged metal in about one milisecond. And–no–it is not possible to look at a timing belt to determine if it needs to be changed. It can look pristine and can snap 5 minutes later, thus causing valves and pistons to collide, and the engine to immediately cease functioning.
Replacing the timing belt, the water pump, the serpentine belt, and all belt tensioners will likely run about $500, but if you don’t do it, you will have to pay that $500 + a towing and repair bill of perhaps ~$2k when the belt snaps. Clearly, it is not wise to skip this service, so unless you have documentation that the timing belt was replaced already, you need to have it done a.s.a.p., as the current one is living on borrowed time.