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Working on dialing in my idle parameters on my 95 w/ MSPNP2, and having an odd intermittent issue. Occasionally, seemingly after an unusual power cycle of the ECU (stalling it, switching "tuning" devices, etc) the car will have an idle hang issue after letting off the throttle. Looking at the Idle PWM %, shortly after letting off of the gas, the Idle duty will shoot up to about 75% of the usable range, hang for a bit, and then fall back down. Of course this causes the RPM's to rise (as if you're holding the throttle; to around 2000RPM). To "fix" this, I normally make a small change to the Idle PWM limits, and resend to the car, change them back, resend, and all is well. Below are my settings I'm running now. I've gone and found the upper and lower limits using the test mode. But was hoping for some insight on some of the other parameters if there is room for improvement. Appreciate the help!
When he says MAT table, he means use initial value and then tune using the MAT for the look up. You can use MAT or CLT, I like coolant personally. To tune it initally, get the car warm and start the idle valve test. Get the values for the specific RPM. Plug those into whatever Mat/CLT you choose
When he says MAT table, he means use initial value and then tune using the MAT for the look up. You can use MAT or CLT, I like coolant personally. To tune it initally, get the car warm and start the idle valve test. Get the values for the specific RPM. Plug those into whatever Mat/CLT you choose
I followed his suggestion, and started looking through the table. Mine shows like this by default. When you say "get the values", I assume you mean put the IAC in test mode, and note the Duty % that yields the RPM's along the X-axis in the below, and list those for each respective RPM? What's the significance of MAT in this? And Why does/would the Duty % change with engine load for this parameter? Thanks!
You got it! What Idle % is required to hit your desired rpm. MAT or CLT would be which row you enter those values into. As you decrease in MAT or CLT you generally need a little more IDLE % in that row. Make sense?
You got it! What Idle % is required to hit your desired rpm. MAT or CLT would be which row you enter those values into. As you decrease in MAT or CLT you generally need a little more IDLE % in that row. Make sense?
I follow. So is the y-axis MAT/CLT in that case? Rather than load?
Yep! Its whatever you tell it to look up in the closed loop idle settings
Would you mind including a screenshot of yours when convenient? Just to get an idea of where to start with how much to scale up with temperature? Appreciate all the help!
It's all going to be different man, no point in including mine. Go out and do it, it will seem less weird and scary once you get some experience doing it I scale up by one click on the up arrow. See if you need more or less
It's all going to be different man, no point in including mine. Go out and do it, it will seem less weird and scary once you get some experience doing it I scale up by one click on the up arrow. See if you need more or less
10-4 on that. I guess I'm curious what to look for. If i set all my base numbers based on the manual idle valve testing at "ambient", will the idle want to sag at that same RPM when it's hotter? If so, just add a click or two to meet the target number again?
Yes, using the idle initial value table is the way to go.
I recommend you take a log from cold and drive around a little. As you are warming up, stop the car every few minutes and let the idle stabilize and then continue on for a while.
Keep doing this and you will be logging the optimal PWM % while warming up. The stable idle values will basically map to a diagonal set of cells in the initial value map while the PWM values related to the RPM drop to your target idle values is also handy for populating the areas outside of the diagonal cells - they may be lower than perfect as the values are continually trying to reach your target idle RPM but they should be close.
Take the numbers from your log and populate the table at the {RPM,MAT} mapped cell. I would add a couple of % to give you a landing pad.
You might not have full coverage, however you can interpolate/extrapolate the unknown numbers.
Now going against popular opinion: I use a y-axis of CLT, not MAT.
The reason is I live in a cold climate and using MAT does not provide behaviour I am happy with.
For example: in winter ambient may be -10C and my CLT could at a normal running temp (90-95C) but my MAT could be 10-15C. In the summer, MAT would be 40-45C.
This causes my RPM entry to idle, in winter, to be way too high. I find CLT provides much more civilized behaviour . YMMV
Last edited by VcrMiata; 06-04-2019 at 08:44 PM.
Reason: minor change on last line
I do it looking up CLT and test it at operating temp which is the top row. I add idle % as I have colder coolant I can't speak for hotter mat than what you test at, but i would assume the idle % goes down from where you test, yes.
Now going against popular opinion: I use a y-axis of CLT, not MAT.
I don't think thats against the popular opinion personally. Also I agree, where i live the Mat doesn't change as much as my coolant does on a daily basis
CLT does not account for IAC heatsoak. As IAT's rise you need more valve duty. Summer is the same for everyone.
The way I see it you have 5 rows to account for all situations, even freezing temps.
If you are getting IAC heatsoak you have other problems or conditions that I do not. Summer is also not the same for everyone. I'm not going to argue with you.
OP use whatever variable you like, that you feel with be the most applicable to your situation and use for the car. Try MAT and CLT and see what you like.
CLT does not account for IAC heatsoak. As IAT's rise you need more valve duty. Summer is the same for everyone.
The way I see it you have 5 rows to account for all situations, even freezing temps.
I respectfully disagree.
The main problem is that I have found newer firmware does not use idle target RPM to pick a value from the initial value table. If it did, I would agree with you; as the table could then be constructed using MAT to pick a nice value: it would be a blend of MAT and CLT (based on idle target RPM). However, I have found it uses current engine RPM to initially index the table. i.e. If my initial value table x-axis RPM goes from 800 - 1300, when decelerating from speed, I find it always enters the table when engine RPM drops to 1300 and therefore picks a MAT indexed cell with a PWM that is way too high (a target idle RPM of 1300 would normally mean CLT is very low).
Also, I have found that idle initial values, for me, are independent of heatsoak; I find AFR is greatly impacted, not so much idle duty cycle.
I handle heatsoak by disabling MAT during ASE, increasing my ASE fueling when hot and extend ASE taper to be active _much_ longer. This has worked very well for me.
Note: I reported the issue with the initial value table not using the target idle RPM to index the table a couple of years ago @ msextra. I found a workaround that is good for me and if someone says it's been fixed, I may just try again as I really would like the initial value to take into account MAT and CLT.
06-04-2019, 06:00 PM
Occasional Floating Idle on Decel
0
. YMMV
