TT IAC Questions (and more)

[Drweldin]

First, long story -short;
I have been fighting a rich idle condition for while,and decided to
play around with Fixed SAS and BISS screw to see if I can adjust
it out.....well I am getting close,but had a few issues:
1) IAC counts go to ZERO when warmed...this is even after adjusting
per the manual. IAC seems to function normally otherwise...bumps up with
steering input,AC,etc...coil also test good with multi-meter per manual...
Question: what would cause this?
2) Also, I have to adjust idle to 900-950 range to accomplish 14.7 @ idle...don't like this, but seems to be a "is what it is" thing...
3) Now when coming to a stop, idle hovers at 1600 then eventually drops to the 950...annoying, and Im sure has something to do with the adjustments I made...tried to back off the dashpot a bit, but seems about the same...throttle cable seems fine....
Any ideas ? Any input apprciated!
Thanks!

[Drweldin]

Should clarify- 560cc EVO injectors, MAFT Gen 2, 3.5" GM MAF in blow thru, twin dejon intakes.....

[Bret Brinkmann]

I take it you could not tune it lean enough with the MAFT with out messing up the rest of the tune? How rich is "rich" anyway?

1) Your IAC counts are being effected by the setting of your BISS and MAFT. Regaurdless of what you want the ECU is going to adjust the IAC to get what it wants to see. It wants the engine to idle around 800-875 rpms and will adjust the counts accordingly.

2) Sounds like your ECUs fuel trims are maxed out. The source of all of your AFR concerns. Do you have anything to adjust fuel pressure with? If so, what is the base fuel pressure at now?

3) The dash pot is to help prevent stalling and sergeing when the throttle is closed. The higher idle should happen normally, but it shouldn't be that high. If we can get your other concerns squared away, that should resolve this problem as well.

[Drweldin]

Originally Posted by Bret Brinkmann

I take it you could not tune it lean enough with the MAFT with out messing up the rest of the tune? How rich is "rich" anyway?
No- adjusting the MAFT does nothing to AFR @ idle....unless I go dramatically in either direction....and even then AFR doesnt change, just runs bad...if that makes sense

1) Your IAC counts are being effected by the setting of your BISS and MAFT. Regaurdless of what you want the ECU is going to adjust the IAC to get what it wants to see. It wants the engine to idle around 800-875 rpms and will adjust the counts accordingly.
I have no problem adjusting the idle to 750 or whatever the spec is, but the AFR is rich (11-11.8 depending...)I should note: even at 750, IAC counts go to zero...but IAC seems to function normally otherwise...
2) Sounds like your ECUs fuel trims are maxed out. The source of all of your AFR concerns. Do you have anything to adjust fuel pressure with? If so, what is the base fuel pressure at now? Yes, AEM AFPR...adjust to spec...35...at the moment lo trim is -81, mid is -84, Hi is 100.....but yes, lo never moves
3) The dash pot is to help prevent stalling and sergeing when the throttle is closed. The higher idle should happen normally, but it shouldn't be that high. If we can get your other concerns squared away, that should resolve this problem as well.
I took the TB apart to check O-rings, etc..reset Fixed SAS....it all looks pretty good, may have helped this a little bit...actually replaced the lower intake (stripped holes) and everything looked good there too.....car runs pretty dam good....just idles rich, and IAC counts

[Bret Brinkmann]

What are the IAC counts when the car is cold? Have you checked the IAC port to see if it needs cleaning? It looks like the ECU is trying to get more air into the engine but just can't do it. Maybe a leaking injector? Try a fuel pressure leak down test. On a side note, do you have any head work done?

[Drweldin]

Originally Posted by Bret Brinkmann

What are the IAC counts when the car is cold? Have you checked the IAC port to see if it needs cleaning? It looks like the ECU is trying to get more air into the engine but just can't do it. Maybe a leaking injector? Try a fuel pressure leak down test. On a side note, do you have any head work done?

WHen the car is cold, counts are fairly high, and the car will idle somewhat stoich when cold...its not unitl it warms up that counts go to zero, and idle gets rich (coolant sensor is new)...also, idles stoich when AC is on because IAC counts go up...with AC on (as they should)...I didnt look "inside" the port if thats what you mean. IAC tip was pretty dirty, so I should check it out...I think the idle is rich because there are no IAC counts....correct me if Im wrong, but the counts displayed are a command of the ECU, not any ref. to the IAC itself(?)In other words, would it be worth replacing the IAC to see what that does?
Injectors passed leak down test at Cruzin Performance (twice)...btw, there is a debate going on behind the scenes on whether or not EVO 8/9 injectors cause a rich idle, because it seems to be fairly common....although one could attribute that to the fact that alot of people are using them - not sure...
Head work? yes, I ported/polished the heads when I had the VSS and guides replaced, but the problem was there before, exactly as it is now....

[Bret Brinkmann]

Replaceing the IAC wouldn't change anything. It is letting in all the air it can but you are still too rich. You need some thing to adjust the AFR at idle like an SAFC. But don't gett a NEO SAFC, every car I have seen with one of those has a really odd fuel curve that can't be tuned out.

[Drweldin]

Originally Posted by Bret Brinkmann

Replaceing the IAC wouldn't change anything. It is letting in all the air it can but you are still too rich. You need some thing to adjust the AFR at idle like an SAFC. But don't gett a NEO SAFC, every car I have seen with one of those has a really odd fuel curve that can't be tuned out.

I have a MAFT Gen2....I can't tune it out....hence the problem...I see trying different injectors as the next step at this point....we'll see

[TurboBob]

what are your trims?

what is your fuel pressure at idle?

what are your tune settings?

what is your output frequency at idle?

the hanging idle is most likely the dashpot.

[Drweldin]

Originally Posted by TurboBob

what are your trims?
81 / 81 / 100 at the moment...lo rarely if ever moves, mid is
usually in upper 80's, but 81 now, hi will usually settle into the
lo 90's, but is 100 right now...
what is your fuel pressure at idle?
36 or a little more...(gauge at rail reads a little lower than in car gauge,
rail is 36...in car is 40...

what are your tune settings?
-36.5 mainscale, -.5% @ 800 (lo) so -37@idle...otherwise I pull
a little fuel from 2800-5000 in both mid and hi map...

what is your output frequency at idle?
31 Hz (On the logger)
the hanging idle is most likely the dashpot.

I will check again, but I dont think its even doing much at this
point....I adjusted it back pretty far....