So on the ECU differences, I just found a 91 Miata with front end damage, but runs and drives that is cheap ($800) which would be an excellent drivetrain donor if we wanted to convert to a manual. Probably part it out and recoup much of my costs here. So, if you do a manual conversion, can you just swap to the manual ECU or are they different?
I don't have an absolute answer, but the wiring harnesses are different between auto and manual cars, so likely not. Also, as Keith noted earlier, the auto uses a different type of TPS which would also indicate not being able to just swap ECUs.
There's a missing sensor on the trans as well - neutral switch, maybe? IIRC there's a writeup from someone who's actually done it on Miata.net. I mean, we've done it at FM, but we had to install a T56 and a V8 to get the job done 
Thanks for the additional info. It looks like while the swap has been done and is relatively straight forward, the best way is to either find a parts car and swap everything over (including the main wiring harness and ECU) or try the list of "fixes" for the CEL and other minor issues that crop up after the swap is done. I have found a wrecked 91 with 84k on it and could just swap the entire drivetrain (engine included) and the wiring harness and part out the rest to recoup my costs.
I am thinking that my best course is to detail the car and flip it later this year. Car is totally rust free, which is pretty amazing, must have been garage kept it's whole life, has a hard top and just needs paint to be a really nice example of a stock NA.
Both of the kids want to learn how to drive a stick, so if I flip this one, I'll go find one that already has some of the good stuff on it 
Keith Tanner wrote: It's a proper 0-5v potentiometer, not just two switches as found on the stick 1.6 cars.
That's because there's only two throttle positions in a 1.6 manual Miata - idle and flat out! 
You'll need to log in to post.
