Check engine light stays on now after new plugs.

[adjuster]

Okay, I pulled the OEM 4 ground strap plugs, with what appears to be the indicated miles on the Odometer of just under 75,000 miles. They were all coated with light brown soot, one has some blistered soot build up, that appears started to flake off, but no oil or signs of detonation.

I replaced them with Autolite Iridium plugs, that also have a small platinum pad on the single ground strap.

Noticed that one of the coil packs did not look like the others, and appears older than the other 7. Same type however, 4 pin, and this is a 2001 S8 with the 40V 4.2V8. (USDM.)

So, it started up fine, slight miss for a moment, then smoothed right out. Took it for a drive, and it ran fine, punched it, and the engine light flashed.. (It's done this before, but only when I'm pushing the car past 120mph for extended periods of time. flashes, but then stops when I slow down to under 120mph... )

Well, this time, about 80mph, it flashed like before, and now has stayed on.

I have replaced some of the vac lines with the woven cover, as they were cracked and while not leaking, crumbled on contact with my hands/fingers, and failed when I removed it from the fittings.

Question is, are these plugs a bad idea? I'm reading here that most folks use the OEM plug, with the 4 ground straps and large electrode. I have never had issues with irridium plugs before this, and on all the other vehicles I've used them, they work great.

I'm going to change out the rest of the vac lines. (I need to buy some more hose, I used what I had in the garage to replace the lines that looked the worst.)

I don't have a VAG Comm yet, but am looking to buy one. Where is the best place to get one in the USA?

Thanks, and sorry for so many questions.