Mx5 NC1 1.8 Manual Idle Issue.

[@NG_MX5 Niall]

Hi everyone.

Im looking for a little bit of assistance as I'm quite new to mapping.

I have a single car software license and I'm trying a couple of maps and getting the same issue across the maps.

My standard idle when I am stationary is fine.

However when I am moving even at 2mph, either in or out of gear, with the clutch fully depressed or otherwise, I'm seeing my revs drop to about 550, then shoot back to 950 ish (baseline) then constantly repeat.

This was not something that occurred before the maps. And I have changed no hardware before or after remapping. It's also very odd that while I'm slowly rolling it will keep on dipping, but the moment I stop, it holds stable 950.

I have also kept the same (performance only) map on the car for about a week now with regular driving just in case the ECU needed to re-learn.

So all fingers are pointing to an oddity in the map file.

Other perhaps helpful info.

Stoichiometry reads completely fine.
Plugs only have about 6k miles on them.
Direnza air filter.
Aftermarket backbox only.
Base model no AC (I've read that this might throw some odd errors).

Thanks for your thoughts everyone .

[mituc]

Can you please take a log when that happens? Make sure you log both short and long term fuel trims, engine RPM, timing advance, throttle position, and if you have available on the platform also the desired throttle position.
I assume this issue is not present with the factory tune, right? What about the stock tune from Versa?

[@NG_MX5 Niall]

Can you please take a log when that happens? Make sure you log both short and long term fuel trims, engine RPM, timing advance, throttle position, and if you have available on the platform also the desired throttle position.
I assume this issue is not present with the factory tune, right? What about the stock tune from Versa?

Thank you for getting back to me. I'll look into trying this out. I've barely poked around in the software yet so I'll see what I can suss out while I'm at work tomorrow my friend.

I think I know how to add things onto the log. But it might take me a bit to figure out... My apologies.

And I know the tune which was on the car when I got it (100k miles on the clock) didn't have this issue. I assume that it was a stock map as the car was almost entirely stock.

I'll report back with my findings my friend.

[@NG_MX5 Niall]

I've got set up on the dashboard the following parameters:
Long term fuel trim
Short term fuel trim (primary)
Short term fuel trim (secondary)
Ignition Timing Advance
Vehicle speed
Relative Throttle Position
Desired Thtottle Position
Engine RPM
Desired Engine RPM

I'll see if I can record a good log on the way in to work tomorrow (roughly 20 min drive) I don't know if that will be too long?

I can imagine I can replicate the issue with the cold engine in a very quick couple of trips round the industrial estate where I work which would be much more sensible in file size etc.

I will report back with my findings 🫡

[mituc]

I'll see if I can record a good log on the way in to work tomorrow (roughly 20 min drive) I don't know if that will be too long?

Only catch the problem in that log. If it can be reproduced then start logging before triggering the problem, trigger it, stop logging 4-5-10 seconds later. If you take a 20 minutes log you'll have to find those 5 lines of interest within those 10k.

[@NG_MX5 Niall]

Good news, I managed to get a solid (short) log of the issue. I'll be uploading here in a mo for review. I just have to hook up the lappy to the wifi here.

[@NG_MX5 Niall]

Here is the log file in question.

Hope this helps find the issue.

[mituc]

Ok, so you have a huge vacuum leak, it can be anywhere after the MAF and the head (including the intake manifold gasket). You need to check everything in that area.

Fuel-trims.png (140.58 KiB) Viewed 226 times

[@NG_MX5 Niall]

Oh really?!!! Wow. OK then! That helps nail things down I'll give it a thorough going over! Thanks so much for your help my friend

[@NG_MX5 Niall]

Nothing evident that I can see on the vacuum leak. It's very hard to replicate too. Especially on my own, as I can't Rev the car with my head under the hood. And everything looks tight and well sealed.

Again, this issue only occurs when the car is rolling and never when stationary. I'm going to try and get some carb cleaner to spray around the intake seals and see if I have the revs climb at any point.

This is super frustrating...