MS3 RPM Dip
 

Hey All,

This has been a consistent problem for me that I've never been able to solve. I've tried a number of things suggested on this board but still can't nail the reason why my car decides to idle fine (900RPM) then dip to 400RPM sometimes. This only happens when the car is warming up. Once the car is warmed up however, it no longer experiences this problem.

On top of this all, when its rainy or cold outside, sometimes (infrequently) the car decides to rev up to 4000RPM. So I can have my gas off the foot and it begins to accelerate. It hasn't caused me an accident yet, but it almost drove me into a parked car once. Again, I'm not able to capture this instance during a datalog.

Here's my MSQ, MSL files.

2003 FM2 turbokit, MS3 (Rev), VE map has been dyno tuned, but I've adjusted some numbers to smooth it out.

https://www.miataturbo.net/attachmen...ine=1453788216

**Edit: my AEM wideband sensor failed recently, another one is on its way. This problem has been here since I installed the MS3**

Captain Obvious here, without looking at the MSQ.. how much have you poked your idle settings? It sounds a bit like mine until I finally read a bunch of threads and got a grip on closed loop idle.

I've asked a fair number of questions and couldn't figure it out. The last time I tried working with this problem I was wondering whether my MS3 was wired properly. My min duty = 32%, max=100%, which is supposedly far off from the 20-64% people see with the 99-2003 Miatas.

I've been fiddling with my MSL all night and found something interesting. When my battery voltage hits 13.5, I begin to get the surges in my PWM Idle duty from 52% (idle) to 75%+. I'm going to apply a correction to see if I can reduce these surges. It's at these surges where my RPM dips to 400 and sometimes stalls out.

Not sure If that's the right logic but I'll play with it.

You're close.. voltage, load, all of it comes into play with a dip that unsettles idle. There are two major components to getting closed loop working. 1 - make sure it's entering at the right time (not locked out), and 2 - is the PID settings that are less important than you think. My problems were mostly from getting locked out, especially on cold starts.

I'd start with a lower max duty though - that's part of why it's spiking to 4000. I'd like to be more help but I don't think I have any of my msq's on my computer right now.

My problem has always been with the min/max duties-- they've never lined up with the 23-64% other valves are set at. I arrived at those numbers when I do a valve test and find that 32% my valve is fully closed and 100% it's fully opened-- it actually goes above 100%, which doesn't make too much sense to me....

I'd love to see your MSQ if possible.

Well, you're in luck. Looks like I emailed it to myself from my tuning laptop and it was named working_idle.msq. IIRC, this was leaps and bounds ahead of where my idle was previously and helped me focus on some more cold start issues which unfortunately ended up being my head.

that's cause you have an NB and youre trying to copy others NA valve settings... 30-100 is in line with NB idle valve settings. 20-60 is in line with NA.


the dips in RPM look like a mechanical problem or something with your sensors, and nothing to do with idle settings. As bad as your idle valve settings look based on that log, I'd be looking elsewhere.

Your idle settings are pretty much useless anyway since your idle valve PWM% has little to no effect on your idle speed -- like seriously might as well unplug that thing because it aint doing squat.

I see MAP spikes that correlate with large swings in the RPM and a voltage drop just before it dives down to half the speed. Does the motor actually even run at half the speed, or is the MS just reporting it?

This is what i'm finding now.. my PWM Idle duty either sits at 65% or jumps to 75%-85% (can't figure out why). When it jumps to 75-85%, my fuel map doesn't compensate for that change so quickly and it begins to go extremely lean-- hitting the 200rpm (all this occurs when I lift my foot from the throttle, ONLY WHEN ITS NOT AT OPERATING TEMPERATURE). I'm trying to add more fueling in these cells at the moment and see if I can mitigate such a heavy dip before CL idle kicks in.

The motor also runs down to half speed, it's not just MS3 reporting it. It bogs and will stall if I don't add throttle before it dips below 200.

The only problem with my sensor being off is that my car was running fine right before I installed the MS3. So unless the installation coincided with the sensor fault then we might be able to rule that out. Which sensor should I be replacing if it is a sensor?