I just thought I'd throw this out in case it could help someone.

The idle control valve didn't like a pwm freq of 1kHz, it made strange noises. I set it back to 100Hz and it sounds normal again.

 

According to this post, for 99+ years it's 500hz. I think mine set to 1khz now - will have to back it down.

MX-5 Miata Forum - What is the stock PWM frequency of a '99+ idle motor?

 

So, does anyone have the numbers for NAs?

 

Just set it where it doesn't make the air compressor noise. On my car for the 94 it took 1khz, but other people have had to adjust it around some to get a frequency that worked out. The CPU cycles at 200hz, so you get the best resolution at 200hz or above, but 100hz works ok too.

 

I think the the valves are different between the 1.6 & 1.8 NAs.

I'll try 200Hz and see if it likes it. It could be mine is slow because its got 275k miles on it.

 

The idles valves are also different on the 1,6 and 1,8L NBB models.
I'm running with 1kHz for my 1,6L NBB, while the file I received for the 1,8L whas set to 100Hz.

 

Does that make 4 different valves then? NA 1.6, NA 1.8, NB 1.8 & NB 1.6.....?

I tried 200Hz and it didn't like that either, so I'm back to 100 Hz.