Idle tuning tips
 

First some details about my setup - its in an mx5 based kit car I'm building not actual mx5.
1.8bp engine
diy MS2 running diypnp turbo basemap (afr and spark) ran autotune VE at idle and moderate driving but no WOT yet.
No IAC valve
TD04 turbo on diy manifold with small intercooler
380cc yellow rx8 injectors
AEM wideband (setup as custom linear wideband)

Starts ok from cold and runs a little rough as expected with no IAC valve but after a minute or so it idles quite nicely. When it gets up to full temperature it splutters and missfires a lot (once per second) although still maintains a reasonable idle (900rpm +/-30). AFR of 13 although the needle fluctuates. If I give it some revs it continues to splutter under no load but when actually driven in gear it doesn't. It drives ok - leans out on sudden acceleration but I want to get idle sorted before I worry about that.

Anyway I've tried giving it more or less fuel around idle and advancing and retarding the spark and none seem to improve it which leads me to believe that it might be issue with setup or even hardware (coils dodgy when hot?).

Any suggestions?

Other thought was I have a v band on the downpipe upstream of the wideband sensor and perhaps these don't form a perfect seal leading to false readings? Here is a pic of the setup. Ignore the tiny air filter - that was just to keep the dust out while building and has been replaced with proper one Note that I haven't finished the exhaust beyond the downpipe.

https://www.miataturbo.net/attachmen...ine=1406484966

The location of your wideband sensor is less than ideal, and it will not give accurate readings especially at lower loads and idle. I would expect readings to be leaner than actual, really way leaner than actual at idle and light cruise.

If it clears up while driving, then I would doubt secondary ignition problems. However, I'd also clean up the high tension leads and install them in the combs to ensure they make no contact with the valve cover.

Lean spike when transitioning to throttle is AE and generally can not be tuned until after the fuel table is. Also bear in mind that there is a slight delay in wideband reading.

Past that, you will need to post a short datalog and a copy of your current tune for further assistance.

Nice car, you should show more pics.

There is a msq at the bottom of the message. I can run a datalog tomorrow.
Where would be a better location for the wideband sensor?

Where it is, but with an exhaust behind it, the problem with your current setup is you'll get fresh air reversing into the exhaust. Closer to the turbine will mean its likely to cook. You can mitigate this with heatsinks.

You're not getting a true AFR reading, it'll be way out, so any minor changes to the fuel table you're doing won't really have any effect.

I wont clog the message up with all my pics but here's a few:
https://www.miataturbo.net/attachmen...ine=1406493524
https://www.miataturbo.net/attachmen...ine=1406493311
https://www.miataturbo.net/attachmen...ine=1406493311
https://www.miataturbo.net/attachmen...ine=1406493311
https://www.miataturbo.net/attachmen...ine=1406493311

Ah that makes a lot of sense actually! Oh well looks like I'll be leaving the tuning til the 'zorst is finished. Which is a bummer since I can't get my hands on a welder for a couple of weeks.

Looks like a real nice car. I have found difficulty getting back into Miatas after driving Westies, Exocets, and Locosts.

Your fuel and spark tables go only to 100kPa. I hope you've been staying out of boost.

Thanks I didn't realise! Although I've been taking it easy. I'm glad you let me know because I thought that y axis was always scaled between 0 and 100%

Yea the y axis is % load, whatever that load may be set up as, Kpa, TPS, MAF etc.

Car looks great btw, where are you in the UK?

Thanks. I'm in Germany with the forces actually but I'll trailer it to UK for IVA test. Looks pretty complete but there's still a fair bit more work to do on it before I'm ready for that

reinstall the idle valve and/or load gslender firmware and use timing to control idle.

Idle valve does seem to be fitted, you can see it in the pictures.

No I lost the idle valve when I moved or else its hidden itself bloody well. Are all 1st gen idle valves compatable? Time to jump on ebay again I think.