Help with PID controls for IAC.

[joecar]

They should be quite close.

Idle tuning is one of the more difficult tasks.

Post new logs and scteenshots as you proceed.

[Ben.]

Made a bit more progress yet again. I absolutely raped, pillaged, stole from and set fire to my "IAC steps vs effective area" to bring my desired airflow into line with my dynamic airflow at idle. This did very little, but in my mind was a step in the right direction. By this I don't mean fudging the IAC map, I'm certain it was the wrong way to go about it, but bringing dynamic and desired into line has to be doing good things for me.

After that I started adding throttle follower back in, and now my IAC is doing exactly as I wanted it to, and it returns to idle at a reasonable rate now. It's not too slow but it doesn't plummet straight passed desired RPM either. At this point my Proportional, Integral and Derivative values are not too far from stock, as opposed to the hacked up mess they were before. This has also helped with another issue, which was hunting when engaging the clutch, as the PID's before were hacked up to catch the idle after a free rev, they seemed to struggle with finding the right rpm when under load.

Now the issue I'm facing is (and has been half the battle all along) oscillations just off idle. As the idle is slowly coming down, it gets to about 1200rpm and starts oscillating up and down, maybe 5 times before coming to a stable idle. It also does this when starting the car, basically under the same conditions, from the added airflow from cranking, it slowly dissipates, and as revs drop to around 1200rpm, it starts oscillating a few times before coming to a stop.

It used to do it before with light throttle, which it still does it now, just much less. The only way I can get rid of it is to drown it in fuel till it starts to bog down, which smooths it out. Tried all manner of fuel and timing, nothing seems to fix it. I don't have a wideband fitted to the car, but I know I'm pretty close, as I can use Bi-Directional controls to take and add fuel in most places and feel where it goes rich and lean. I have actually noticed in a couple of other tunes that the tuner has done something similar, throwing lots of fuel into one or two cells to richen it up (I remember exactly because it was also in the 1200rpm column). Going to try that tomorrow, laptop died today before I had a chance to have a crack.

[statesman]

Now the issue I'm facing is (and has been half the battle all along) oscillations just off idle. As the idle is slowly coming down, it gets to about 1200rpm and starts oscillating up and down, maybe 5 times before coming to a stable idle. It also does this when starting the car, basically under the same conditions, from the added airflow from cranking, it slowly dissipates, and as revs drop to around 1200rpm, it starts oscillating a few times before coming to a stop.

It used to do it before with light throttle, which it still does it now, just much less. The only way I can get rid of it is to drown it in fuel till it starts to bog down, which smooths it out. Tried all manner of fuel and timing, nothing seems to fix it. I don't have a wideband fitted to the car, but I know I'm pretty close, as I can use Bi-Directional controls to take and add fuel in most places and feel where it goes rich and lean. I have actually noticed in a couple of other tunes that the tuner has done something similar, throwing lots of fuel into one or two cells to richen it up (I remember exactly because it was also in the 1200rpm column). Going to try that tomorrow, laptop died today before I had a chance to have a crack.

Someone over on LS1Tech thought it was a good idea to do an open loop idle instead of learning how to tune closed loop idle properly... and now everyone's doing it.

[joecar]

Made a bit more progress yet again. I absolutely raped, pillaged, stole from and set fire to my "IAC steps vs effective area" to bring my desired airflow into line with my dynamic airflow at idle. This did very little, but in my mind was a step in the right direction. By this I don't mean fudging the IAC map, I'm certain it was the wrong way to go about it, but bringing dynamic and desired into line has to be doing good things for me.

After that I started adding throttle follower back in, and now my IAC is doing exactly as I wanted it to, and it returns to idle at a reasonable rate now. It's not too slow but it doesn't plummet straight passed desired RPM either. At this point my Proportional, Integral and Derivative values are not too far from stock, as opposed to the hacked up mess they were before. This has also helped with another issue, which was hunting when engaging the clutch, as the PID's before were hacked up to catch the idle after a free rev, they seemed to struggle with finding the right rpm when under load.

Now the issue I'm facing is (and has been half the battle all along) oscillations just off idle. As the idle is slowly coming down, it gets to about 1200rpm and starts oscillating up and down, maybe 5 times before coming to a stable idle. It also does this when starting the car, basically under the same conditions, from the added airflow from cranking, it slowly dissipates, and as revs drop to around 1200rpm, it starts oscillating a few times before coming to a stop.

It used to do it before with light throttle, which it still does it now, just much less. The only way I can get rid of it is to drown it in fuel till it starts to bog down, which smooths it out. Tried all manner of fuel and timing, nothing seems to fix it. I don't have a wideband fitted to the car, but I know I'm pretty close, as I can use Bi-Directional controls to take and add fuel in most places and feel where it goes rich and lean. I have actually noticed in a couple of other tunes that the tuner has done something similar, throwing lots of fuel into one or two cells to richen it up (I remember exactly because it was also in the 1200rpm column). Going to try that tomorrow, laptop died today before I had a chance to have a crack.

Ben,

Just playing with it is helpful as it gives you more insight to how it works ... if only we had more time to spend

Post your tune file so we can have a closer look (can you also post your stock tune file).

[Ben.]

Someone over on LS1Tech thought it was a good idea to do an open loop idle instead of learning how to tune closed loop idle properly... and now everyone's doing it.

Agreed, I know closed loop can work with cams much bigger than mine, and it is indeed on my list of things to do, however I want to get it running better without all the corrections taking place, then ad them back in. If you can provide any helpful hints or tips for closed loop fueling at idle, I'll gladly listen. I was actually playing with it a little a while ago, by changing my switching points I could get a decent idle (once it settled) but if it was swinging back to its lean side it would stumble if you hit the throttle at that moment. So I'd decided that for now, I'd let it idle a bit rich in open loop, and use the factory switching points to maintain fuel economy when it's being driven. When I get back to it, my next approach will be to leave the switching points and play with the 'closed loop proportional idle' settings, and use this as you would any other Proportional and Integral terms, trying to keep the o2 voltage pretty centered rather than swinging each side of its target value. Anything else you can suggest before I head this way?

Ben,

Just playing with it is helpful as it gives you more insight to how it works ... if only we had more time to spend

Post your tune file so we can have a closer look (can you also post your stock tune file).

100% agree, I'm taking this as valuable learning. A lesson learned hard is one not soon forgotten. I bought this car already 'done', it just ran like crap when I got it, much worse than it is now. The guy that tuned it is very well respected in Australia so I was telling myself there must be something small in there somewhere, but as time has gone on, I'm pretty confident some of the main input data is skewed. I would love to licence a stock tune and start fresh, I'm sure this would be a better place to start, however I don't want to spend more money on licences and dyno time, I'll just try to salvage this one for now. All the high load stuff was done on the dyno, just told myself I'd sort out the idle and 'less critical' things in my own time.

I doing my tuning with 'the other brand' so I can't post those here. I'm just here because you guys seem to be (and have been) much more helpful than 'those guys' haha.

[joecar]

You can post .hpt files here for reference purposes, I don't have any problem with that (and we're forever learning more, especially idle).

[joecar]

I'm finding that to save time/effort in fixing already-tuned tunes (containing hundreds of changes), I find that we always end up going back to stock, inserting correct injector data, redoing VE, and then we find idle is fairly reasonable just needing minor tweaking (which also means we don't learn any hard-earned idle lessons...)... and the tune file now has just the changes it needs, no more and no less.

[Ben.]

That may just happen in the not too distant future, but I'm going to try and persevere with this for now. If I was keeping the car long term, that's most likely what I'd do, but I may be selling it in the near future and just want to get it driving nice, preferably without spending all the time and money on licences and dyno time. Although I know it won't be 'right', if it drives good, then I'm ok with that, even if the numbers in the tune look odd. Bandaid fixes all the way!

I've got a couple more things to try (hopefully later today) and will re-assess from there.

Here is my current working tune, it is a HPT file, I just changed the extension to .tun so that it would let me upload it, don't know if it will open in EFILive:
working.tun

[Ben.]

This is where I got to today. It's catching it high enough, but goes into a funny oscillation while its at it. I've got more timing in it now, at idle regions and just above idle, this extra timing at around 1200rpm really helped it catch. I had taken a heap of timing out of this area a while ago to combat some pretty severe bucking on decel. Also added a bunch of fuel right at 1200rpm also to smooth it out a bit.

Kept the log pretty simple, just 3 separate free revving events. I know it's a different scanner to what you guys are used to, but it's pretty straight forward, I'm sure most of you can decipher the data there.

You can see the IAC is doing what I want it to, if anything a little slow but it's following the right pattern at least. Any hints on what I should log to track down that oscillation? Apart from the all too obvious wideband which I don't have in the car?

[GMPX]

Here is my current working tune, it is a HPT file, I just changed the extension to .tun so that it would let me upload it, don't know if it will open in EFILive:

Oddly enough you can't open a file created in HPTuners with EFILive