Bad Idle, I have lots of data that may help.

[mjjstang]

I know this is a long read, BUT PLEASE.... if you can help me I would be forever indebted.

I have sr20det and have never solved my idle problem really. However I have some information that may help you in helping me. Also I am not trying to sound like a DB but please respond only if you have some knowledge about values etc, and not just a hunch that it sounds like someting you had gone through. Trust me I have posted on this a bunch of times on zilvia before I had data, and i Have tried everything that people said they thought it was. OK....

My idle at startup is horrible, it will rev to about 1500 or so, and sometimes stay there for a second, then on its own, or sometimes after I rev it a touch, it will come back down to 1000-1500 and creep down to around 900 and finally just shut off. It is very finickey, If i can keep it at 1500 for a second, or somewhere around there, it will stay for a minute, then trickle down and sputter off.

Now when I am driving, at first the first few minutes it does the same thing, at a stop if I dont keep the revs up, it will shut down. by 10 minutes on the road, it becomes pretty consistant. If I adjust the IACV after this period of time, it responds pretty normal as far as adjusting the idle, however sometimes even after 10 minutes, it will shut down at a stop light etc, very rarely after 10 minutes though.

Now things I know.

Ignition timing...ok
Injector time...ok
Air fuel....ok
air flow(z32)...ok
02.... ok

Coincidentally the two values that seem a bit off are TPS and IACV
These would probably be the two that I would be most concerned about for this problem. I will explain in detail the issue with each sensor.

TPS

with throttle valve fully closed I should have .35-.65 volts
I have about .28 which is close but out of spec.
I could adjust the tps to get .35 or higher, however this signals tps not fully closed, The highest voltage I can get with the "throttle closed" indication is .28 volt. Therefore I will never be able to get within spec. with this TPS setting, at WOT I am around 3.8 v where the manual says "around 4.00 V" so this is out of spec but with the "around" specification, I assume I am close. overall the tps seems to be close enough to not cause this issue I am having. I guess that if I still can not fix this problem, then I will invest in new TPS see what happens.

IACV

This is most likely my problem. The specifications for the IACV at idle is 20-40 percent, and at 2000 rpm "-" I assume it really doesnt matter as it is an IDLE air control valve. Anyway Like I said, sometimes I can get a good stable idle, and this is when the IACV readout will show me increasing and decreasing percentages as I turn the adjuster on it. I had the good idle and adjusted it to 30 percent which was middle of acceptable values. But then when my idle goes to shit, the IACV seems to go haywire and usualy ends at a value of 8 percent, and theres not much I can do to get it out of 8. turning the adjuster gives me a noticable increase or decrease in idle, but the value on readout never changes. One would assume that I have a bad IACV, HOWEVER....

first off let me personify my idle in the sense that it seems to have two personalities, the time it fucks up and the time it is ok, and will tune out to my specifications. I seem to be able to control it by giving it some gas and letting off, there seems to be a sweet spot somewhere, where if I caress it just right, I can get that steady idle, that is why i am not sure if It is the IACV, I would think if it was the IACV, that was bad, it would only have the bad idle, of course the IACV could be bad intermittently, but like I said, I seem to be able to find that good idle with the throttle, not by banging the IACV or something, two different units.

I realize there may not be too many people out there that can help me, and if not I will buy new TPS and IACV but I figure its worth a shot. Thank you for reading this.

[Def]

Provide some background info like what ROM you are running(stock/tuned) and do you have something like an S-AFC hooked up? What size injectors?

[mjjstang]

ahh sorry, Ok aside from already cleaning the IACV, I forgot to mention that.

Enthalpy
z32 maf
550cc
gt2871r
stock head

It has been quite a few years since I got the tune, and I think I remember having a good stock idle before I went tuned. Enthalpy sent me a new chip just in case that was the problem, now I dont know if the injectors could be the culprit but I know each cylindar is firing, Would those injector numbers help me out through datalog, I assume not since I would really need data from each cylindar. not just one number as is shown on datalog.

[Def]

Unfortunately, the cold start map for stock injectors doesn't suit larger injectors well, which I think is part of the issue you're seeing.

Do you have your O2 sensor hooked up, and is it starting to function properly by the time you see the RPMs start dipping?


I'm almost positive this is an AFR related issue, and the roughness you're feeling are lean misfires.

You wouldn't happen to have a wideband or access to one for this would you? It's the most important gauge IMO, and I think it'd tell you a lot about what the ECU is doing.

[1slowS13]

Originally Posted by Def

I'm almost positive this is an AFR related issue, and the roughness you're feeling are lean misfires.

Maybe your fuel pump strainer is clogged? Could be as simple as that.

[mjjstang]

I dont think it has anything to do with a bad part, because after spirited driving, the car pretty much idles fine. Def, I think you are on to something for the cold start map. However Yes I do have a lc-1 wideband, but it is nonfunctional. The bastard took a shit the second day I had it. I really need to check my wiring just to be sure it wasnt my fault. Any more opinions are welcome. I will revive this thread if it falls to the wayside when I can get some good wideband readings. Thank you for your response.

Also def, if possible can you explain to me what this lean misfire is doing, and how it is creating this hole in my idle, like I said the darndest part with this thing is that depending on my rpms and how I give it a little gas, she reacts funny, like I said about being able to get it into that sweetspot where it will idle fine for a while, but yet my TB is opened just the same as it was earlier, but it produces a totally different idle. Thanks.

[RedtopTech]

your dead wideband may be a clue. Extra rich ratios can burn up a sensor pretty quick. I doubt that you have a converter because it would most likely be toast. Pull your fuel rail up and check for leaks.

[Def]

Originally Posted by mjjstang

I dont think it has anything to do with a bad part, because after spirited driving, the car pretty much idles fine. Def, I think you are on to something for the cold start map. However Yes I do have a lc-1 wideband, but it is nonfunctional. The bastard took a shit the second day I had it. I really need to check my wiring just to be sure it wasnt my fault. Any more opinions are welcome. I will revive this thread if it falls to the wayside when I can get some good wideband readings. Thank you for your response.

Also def, if possible can you explain to me what this lean misfire is doing, and how it is creating this hole in my idle, like I said the darndest part with this thing is that depending on my rpms and how I give it a little gas, she reacts funny, like I said about being able to get it into that sweetspot where it will idle fine for a while, but yet my TB is opened just the same as it was earlier, but it produces a totally different idle. Thanks.

I think it's more to do with accel enrichments being off. I've adjusted the cold start ones, but it never seemed to really help tip-in which is where it gets really lean. You'll feel like the car is just bogging down, which is just the motor going so lean that it will misfire more than it actually fires(misfiring due to AFRs at the extreme rich/lean region are just a percentage of the actual cycles).

I've tuned out some of the bad behavior, but it seems hard to completely eliminate it in ROM tunes. It only happens for about 30-45 seconds on my car, but upon a cold start if I don't hit the throttle it'll idle right at the target AFR plus a little rich for cold start enrichment. Hit the throttle and instantly lean, then it'll drop back down and eventually settle out at a proper AFR after some 19:1+ misfiring(it seems almost random - some days it's worst than others).

It was almost completely gone on 93, but on E85 it's pretty pronounced since it does not like to idle at rich AFRs.

[mjjstang]

I just got my speed sensor installed tonight so I think I will go a tank and see what my mileage is, but I will tell you what, It seems that this thing sucks fuel even when driving conservatively.

Now I do have a sard fpr, if I had a leak I should notice that the psi would drop rather quickly, this it does not. It maintains pressure for quite a while.

I am leaning towards an inherent issue with the rom tune.

Do you know about the IACV and why it seems to stay on 8 percent even when I adjust the screw? Like I said, adjusting the screw definitely changes the idle, I just think the sensor is not picking up on it, IDK.

Lets say I am running extremely rich, I dont know what I can do short of SAFMS. And I really do like my 500 dollar piece of tin.

[Def]

I've never seen an IACV hang up like that, so sorry, can't help you there.

I wouldn't be so quick to completely blame the ROM tune. It sounds like you have other issues going on(i.e. no speed sensor - that is a necessary thing).

Do you have a narrowband O2 signal going to the ECU either via the stock sensor or the 0-1V output from your wideband.

[lok]

Doesn't a bad coolant temp sensor also have these same semptoms?

[mjjstang]

both my ecu coolant temp sensor and gauge sensor are working proper. Also how does the speed sensor have anything to do with my idle or ecu? I have swapped it out though and it is working. That was simply a part that was bad when I got the engine.

[Def]

It does tell the ECU when the car is moving so it can engage a faster idle that drops down when the car is stationary. Not sure if it'd cost problems if it wasn't there.