I am doing GWK are 12mm washers ok?
 

I had read that 12mm work perfect is there any truth to that?

what is GWK?
 

what is GWK?

I used two 7/16" washers. They were both very close to 0.91" in diameter and had an inner hole diameter closer to 1/2". Both were 0.074"-0.076" thick. I found them to be a better match for this job than the 3/8" washers. I took my digital caliper into Ace Hardware and measured a lot of washers until I found two that were almost identical in measurement and spec. I think finding two identical washers is the key for this mod to work right. There's lots of variation between the same size washers.

When installing the washers I drilled the holes out to the point that they fit snuggly around the spring retainer nut. Then I added a tiny bit of super glue to hold the washer to the retainer nut. Otherwise, it kept on getting misaligned when I tried to put it on and it would touch the outer idle spring.

That setup has been working well for me. I didn't even have to adjust my idle afterwards. Knock on wood.

I gotta warn you though that it seems like the 97-98 12v's had more issues with getting the mod to work right.