On NGK's website, they recommend several different spark plugs based on type, copper, platinum, iridium, and other's. I purchased the NGK iridiums (NGK 3764) for a 1997 Toyota CAMRY as listed on NGK's website and every auto parts store. They did not work in this motor. It refused to start. Swap back out to the old dual electrode Denso OEM and it starts right up. Put the Iridiums back in, no go. So I purchased the OEM NGK's and it runs fine. I'm not the only one that's run into this problem. It doesn't seem to happen with all of these engines but for some reason, there are many that won't run, or run like s__t using the single electrode plugs. What is the major difference between the two different iridium plugs 3764 vs 6741??? There both listed for this car along with several others. From now on, I'd stick with stock plugs. I know they'll work.The 97 Camrys came out right before Iridium plugs became OE on the vehicles. I also looked at the NGK website, and honestly, I think the NGK IFR6E11 (6741) would've been better matched than the Iridium IX plugs you initially bought.