RPM hang/surging issue - MS3
 

Let me preface this by saying I am by no means good at tuning, so it may be a super simply setting change. Thanks in advance.

Alright, so I've been having this insanely annoying issue for as long as I can remember since I've had my MS3. It seems to bee more prevalent when the car is started while warm, and more so when the fans are on. I'm having an issue where my RPM surges from around 1700-2200. It is not entering closed loop idle because of this. When the RPM reaches the peak, it will cut fuel drop back down. Today I finally decided to diagnose the issue. Although I believe it is unrelated, I had a vacuum leak (I suspect) from the EGR Vacuum Solenoid. I blew smoke in to the intake and it was coming out of the actual solenoid. I have EGR block off plates, and assumed this solenoid was unnecessary so I took it off and capped the vacuum lines.

I attatched a quick log of the issue occurring and my current tune:
Before the surge starts, I revved it, which started the cycle. At the point it stops, I took a ton of fuel from it, which got it back in to CL idle. Then the EGO correction kicked in and added the missing fuel.

You need to tune close loop idle. Idle control is starting with a duty value high enough to send its self into a perperual cycle of Decel fuel cut and return

https://cimg8.ibsrv.net/gimg/www.mia...f185bf1bc7.png

See, I don't understand why it's showing 48.2%... I previously had CL idle set to 'use last value' other than 'use initial value table' and even now, the initial values are much lower than that. And I was under the impression that something outside of the idle settings were causing this because it isn't entering CL idle. Status 2 shows that it isn't idling during the surging.

I'll see if lowering the initial values or some other setting does anything

Alright, so I may have found the issue. My fans turning on will idle up the motor, and I believe I had the duty set too high. I also lowered my dashpot for throttle lift-off. I drove the car today and didn't have the issue. One problem with my idle, however, is that when I have my headlights on, the fans are on, and any other draws make the car stall out while idling sometimes. Just gotta get the PID settings dialed in I believe.

I really dislike the "use last value" setting for long-term use. I've always found that it's great for initial setup, since it will settle on its own values and allow you to log those values, but once you have those logs, you should build an initial values table based on RPM targets and CLTs. That will give you a more consistent idle than the "use last" setting will.

FTFY

CLT RPM curve, then RPM / MAT table of Initial Values. Takes longer, but results are really good.

Oops, yes. Agreed, and mine are actually set up that way, I just forgot. :) No point in having an RPM CLT curve and a CLT lookup.