I had replaced the original denso spark sparks at about 143K miles to NGK Laser IR 4589 (IFR6T-11). I noticed some hesitation and fluctuation at cold starts and replaced at about 194K miles to NGK IR IX 3764 (BKR6EIX-11). I also admit I didn't know there were different iridium plugs by NGK that fit the car. Now I get to the point and my experience with the latter NGK 3764 and i say avoid them or plan on replacing soon after. I noticed heavy hesitation and turns out i had a misfire in cyl 6. After checking connections, coil primary/secondary resistance, I checked the plug and it's gapped at 0.075. Yes I had them gapped properly when I installed them and i replaced it with a used spare i hadn't discarded yet. I went back to the Denso 3353 (SK16R-P11) long life iridium plugs and while i was at it i checked all gaps on the remaining NGK plugs. Each one increased to anywhere from 0.060 to 0.075. This was with just barely over 20k miles on them.

As far as spark wires go, I replaced the original with the NGK ones at 143K miles and they looked fine but I replaced them with the Denso this time around. Original coils.

While I had everything open at 217K miles, still warm engine, i did a compression test and i had 4 cylinders @ 190psi and 2 cylinders @ 200psi. Figured more numbers for people to reference at different miles.

2003 GS300

 

Your post is informative but what engine are you referring to?

I'm assuming 1uz or 3uz...

 

Edited to include model. I have a 2JZ. Thanks