Miata Turbo Forum - Boost cars, acquire cats. - Speeduino https://www.miataturbo.net/ Discussion about Speeduino. en Tue, 02 Jun 2026 23:52:28 GMT vBulletin 60 https://www.miataturbo.net/mt2011/images_td/misc/rss.jpg Miata Turbo Forum - Boost cars, acquire cats. - Speeduino https://www.miataturbo.net/ Tuning troubles with ITBs https://www.miataturbo.net/speeduino-128/tuning-troubles-itbs-111267/ Fri, 01 May 2026 01:36:50 GMT Im *obviously* on a speeduino, its a 92 thats fairly stock. I've only got headers, and right now put some DIY ITBs on recently. I had almost no tuning issues with the stock intake manifold and the car was running almost perfectly, but am really struggling with the ITBs. I'm getting what seems to be a misfire sometimes, but when accelerating it doesn't seem as obvious. I suspect that my spark map is the main issue, but changing that seems to have little effect. I haven't messed with the map an insane amount because I don't fully trust myself to not enter some awful values and mess up my engine too much. The ITBs are on a cut manifold and 3d printed adapters, with GSXR 600 throttles. I believe there is a vacuum leak at cylinders 3 and 4 which I am working on fixing, but my tuning issue seems to be caused by more than just that. On idle, it is shaking a lot and has some blowback out the intake, specifically in cylinders 1 and 4. It seems like it is mostly isolated to cylinder 4, but felt some blowback out of cyl 1 today. It is running a bit rich now because I wanted to try and eliminate the possibility of it being a misfire from being way too lean. I swapped spark plugs and that seemed to help, but didn't fix it. I also swapped spark plug wires and it didn't change anything. I would think that it is maybe my coil packs, but I only had this issue right when I switched to ITBs. I'll upload my tune and datalog from a coldstart if that helps.

I'm kinda a broke college student so can't really justify just hitting it with the parts cannon.
thanks :)
Attached Files
]]> Speeduino graham_na6 https://www.miataturbo.net/speeduino-128/tuning-troubles-itbs-111267/