NefMoto

When i changed my exhaust to 3" with lower backpressuer my idle at warm engine now occilates up and down when i do a first start. It dissapears after a while.. I suspect it is due to lower backpressure in the exhaust and i need to adjust a PID value somewhere..
Any thread I can read more about this here?

/J

I have the exact same problem with a 1.8t wb car.

Fine on cold start until closed loop kicks in, then hunting until coolant temp reaches 89C-90C, ON the dot.

It is repeatable, does it EVERY time.

Cat heating disabled, warmup fueling is dead bang on.. idle trims are 0

tried raising idle torque reserve, no effect. Also tried higher idle rpm up to 1000, still hunts.

Works fine with AC on.

Would post logs but they're huge, i have the whole start cycle from cold to 90C if anyone needs it; I can post it.

I can understand needing to tweak the idle PID, but what is changing over at 90C such that is is fine (other than the thermostat opening)?

If i ever figure out the problem I will post here.

What's been changed hardware wise?  No issues here.

The 1.8t i'm working on has a ton of changes - injectors, exhaust, turbos, etc. so i'm not sure where to start.

Not sure about Jim's car, of course.

What kind of rpm fluctuations are we talking about?

400rpm or so.

injector p/w ok?

Yes. Injectors are fine.

Everything is fine for the first 110 seconds (open loop) and after the motor reaches 90C, which means either the pump is loading the motor just enough to hide the problem after the thermostat opens, or I'm missing something in the ECU.

Exactly my point log p/w from cold to warm up.

Same here around 400 - 800 rpm....  I happened when i changed Exhaust+Intakemanifold. This occured also before i tuned my engine (OEM MAF + Injectors + OEM File) when i had the exhaust system disconnected (O2 sensors connected).
My theory is that the idle is very fine tuned agains the backpressure of the OEM exhaust system..  It feel like a value in a PID loop somewhere need to be adjusted. The "P" factor should be lowered abit.. hmm or maybe more timing advance @ idle to keep it alive.

What is p/w dream3R? 

Back to school.
Backpressure does not change on idle from a bigger exhaust.
Backpressure is restriction due to high flow. At idle even a 2" exhaust is more than sufficient for your engine.

Yes that sounds correct in my ears and I will not argue with that.  ;D  But i have experienced very unstable idle when I example wise took of the headers on my old 5cyl s2.

Sounds a bit like oscillating stalling protection

Is the throttle plate angle jumping ?

Could be caused by a leak pre O2

Maybe rising egt after warmup will heat exhaust enough to close the leak itself

Just a thinking

I have that. What am I looking for? the p/w oscillates along with the throttle plate and timing as the idle PID tries to control the speed. They don't appear to be bottoming out. I can raise the idle to 1000 rpm, and/or increase torque reserve to bring up load, and the problem still occurs, so I don't think it is an injector problem.

And I can't imagine the water pump load alone is enough to explain what I'm seeing.

It stabilizes EXACTLY at 89.5-90C, every time....

If you log on high sample rate you should be able to see what changes first, throttle angle-injector-ignition or even maf. Rpm will follow this change. Might narrow down the search. My car has a rock solid 880rpm idle with or without exhaust, at any temp. Both narrowband and wideband controlled same result.

Thanks, I'll take a peek! Any other insight as to what happens at 90C in the ECU would also be helpful.

There are additive warmup timing maps that are temperaure enabled, and I also have had my car feel like the pedal behaved different/less aggressive during warmup. (On apx 512kb) For example with cold motor I needed to push the pedal over 50% to get any boost and with hot engine it would shift to 30% pedal. I thought it had something to do with load request during warmup, could as well be influencing your idle area. Cant give you any map names from the top of my head, I'll look into it.

Have you tried to fit another o2 sensor from your own car for example? O2 sensors are notorious for messing up idle too...

Because lambda was not reading right.

I zeroed out the warmup fueling maps for 50 (or 60? Forgot what the 2nd to last temp is) and up, no effect. O2s are fine, like I said the idle is rock solid down to 760rpm at 90C

Ignition oscillate a lot during warm up?

But isnt there a map with Idle ignition or is it just as simple to adjust timing in the main timing maps? I want to ad more ingition at idle.. MY theory is that it will be more stable then.

I think you have i vice/versa mate :)

I had similar issue with one Volvo. Warm engine idle was pretty much ok, but cold start it started oscillating. Also it was was worse when AC pump engaged.
Tweaked MAF scaling a bit since the required airmass for this engine was way off with bigger MAF.
Instant success.

Wild guess about nyet's case is KFRLMN.

Im guessing I have too much maf underscaling. Will also recheck KFRLMN

I am having an issue with an oscillating Idle once it hits 90 deg that continually gets worse till it will stall if you leave it. I will include a clip(do to upload limits) from the log from a cold start to when it starts oscillating. It seems that it goes rich first then throttle and timing go nuts. injector on time and DC don't seem to change. I suspect TEMIN which I haven't been able to find in this file. The idle is not bad for the first 880 seconds.

Car is a mk4 jetta 24v turbo 022906032BM 366145