Hey Folks! First of all, massive apologies, as I'm still learning about everything in regards to tuning and consider myself a total newb. Please excuse my ignorance for any of the questions I'm going to ask. For reference, the car is an 01 with a C30-94 rotrex supercharger, ~700cc injectors, and a MS3PNP. And yes, I'm asking about a supercharged car on MiataTurbo. I accept any and all burning at the stake that is necessary

I've gotten my tune significantly more dialed in over the past few months (well, I'm pretty sure I've hacked my way into warm starts working, but I can't complain), and the car has really been driving well...that is...until it got hot out and I started needing to use the A/C.

Symptoms:
- I start the car, and it idles / runs great. AFR's look pretty decent, everything is going well.
- I flick the A/C on, it idles up, and everything goes great.
- Once the car warms up, as soon as it goes into idle, it all goes to hell in a hand basket. The car immediately starts hunting for it's idle and kills itself after about 5-6 cycles.
- I've tried re-adjusting the initial values tables for the idle, but everything looks OK with the A/C off, and it idle hunts (even in Idle Valve test mode) with the A/C on so it's difficult to tune
- I figured..."well, if it runs fine while warming up, maybe it's the warmup enrichment that's helping, and it just needs more fuel". I adjusted up the A/C duty, but it either didn't help or eventually made things worse.

What am I missing? What should I try? I recognize that I'm a complete idiot and probably missing some of the fundamentals, so I massively appreciate any advice.

I've also attached my current tune (don't judge too much) and a log file that includes the car idling and then flicking the A/C on.

I'd really appreciate any advice that you geniuses have.

Cheers,

Mike

 

Another post here solved idle hunting with A/C ... I don't have a MS yet so I got no ideas
https://www.miataturbo.net/megasquir...stions-100256/

 

Hi, I am the OP from that post. I fixed my issue, I suspect it is a bit of a band-aid fix and not a proper one, but it does work for me at least. The main setting I changed was the 'Idle Advance On' setting, scaling it like this in that post by DNMAkinson I linked in my forum post. It looks like your car is at 15 degrees timing, mine is at 14 in the idle region and it doesn't seem to have any issues advancing this much.



The idle advancing caused my car to not get into a loop around the target idle, my car never actually stalled but it also never entered a point where the compressor engaged, so it never cooled when idling.
I also changed my compressor on delay to 750ms, anything less than that will cause my idle to droop to 500-600rpm then recover to 1300, and loop around 1k, never actually engaging the compressor. You may not have to do this if you don't have an idle dip issue when turning the A/C o

I suspect a proper fix for both me and you would include modifying the closed loop idle PID sensitivity/settings, as it sounds like it is aggressively overshooting your idle target so much that the car eventually stalls. Maybe try dragging the sensitivity slider down a bit and see what happens? I would also recommend watching PedXing's PID Controls video a few times, I had to watch it a few times before I somewhat understood what each value does, I still don't really know what I am doing with it. Please keep in mind I am only 5 days in with my MS3 installed but it idles nicely and my A/C doesn't stall the car, but I don't have big injectors or a brotrex.

Hope some of this helps

 

This is really great! Thanks for the help - I'll definitely give this a shot tomorrow. Somehow missed your thread in my googling / searching, so very glad to have the redirect. I've messed with the PID settings a bit to get the car running right when the A/Cs not on, so I'm hesitant to try them again. Will do some more fiddling and report back.