Rom

Hi all,

So in a quest to solve my idle issues, I've spent some time logging and tweaking settings, but I really need some input (or confirmation)...

To cut a long story short, I basically need to target 1100 RPM's as my normal idle. Under normal conditions, AC off, warmed up, I've adjusted everything to give me a steady idle and it works pretty perfect. ISCV demand is at about 4.7% right now. However, my ISC steps sits around 53 steps, which is high, but probably necessary with my massive ID2000CC injectors (this BISS is all the way right now out so can't go any higher on that).

Before my BISS was adjusted in quite a bit and my ISC steps were at 65. When I turned AC on, it jumped to 85 but idled terribly (dropping to 500-800RPM, and almost always shutting off on stopping). Tonight I adjusted my BISS all the way out. My ISCV demand under normal off-AC dropped from 14% to under 5% (and the trims are still adjusting, so will probably come down a little more).

When I turn on the AC now it's much better (idle sticks around 1100RPM), but ISCV demand is still pegged at 15.2% (seems to be the highest it goes), and the ISC steps jumps to 85 still, and can't go any higher (i.e. seems pegged). This has improved drivability under AC (since the BISS is all the way out), but now there is zero tolerance since it can't go any higher. So if I turn a corner, brake and then stop, it has a good chance of shutting off as it can't add more steps to compensate for the Power Steering load, electrical loads, or other dynamic loads.

Basically I believe I've hit the maximum 85 steps on ISC and 15.2% demand. So my questions are:

1) Is 85 steps really the physical maximum with our ISCV's or is something else stopping it from going higher?
2) Is 15.2% really the max demand, or is it ECU controllable (and if I could get demand to go up, could the ISCV go beyond 85 steps anyway)?
3) If I have hit the maximums, and can't adjust the BISS any more, how can I allow more air past the throttle? It's the stock throttle - will any aftermarket one allow more adjustment on idle air control? I'm thinking I could crack the throttle plate open using the adjustment screws, but that doesn't sound idle, or precise (and will slightly reduce the range of the butterfly).

My goal is to get normal idle ISC steps to about 20-25, and on-AC steps to about 45-50, which should give me plenty of headroom for dynamic loads.

Thanks in advance for any help!

S.

CDrinkH2O

iTrader: (7)

What ROM are you on? For example in the 88590715 you need to adjust the target idle tables to bump up the RPM. Max step value is 255.

Rom

Hi,

​​​​​​I'm on 88591715 (speed density). I've tried bumping those values up but the isc step still won't go beyond 85. Since the revs drop way below my set values it should go beyond 85. I know the digital maximum is an 8bit value (255) but can the ISC actually step beyond 85? I wouldn't be surprised if the max number of physical steps on the stepper motor is only around 85..

I also tested by screwing the BISS in all the way to force the ISCV to compensate beyond 85 off-AC and it stops at 85 too.

Thanks!

S.

CDrinkH2O

iTrader: (7)

Did you pull your ISCV out of the throttle body and check it for a full range of movement, at key on and key off?

This one shows one way to check to see if it is moving through the full range (cold to hot) commanded by the ECU:

Rom

Hi,

Thanks for the response! I did do the first check but mine didn't move much at all. I replaced it and the second one did the same thing so I don't think the on/off ignition test is definitive. It does move when the car is started though as the idle does get adjusted automatically below 85 steps (i.e. seems to be working fine under normal idle). In my case, EvoScan itself doesn't show the steps exceeding 85, so if there is an adjustment higher than 85 that is physically possible, then the issue must be in software. I just wanted confirmation of the full step range of the stepper motor (not the digital 8 bit range available in software since if the physical steps stop at 85, programming in 200 wouldn't do anything more than what 85 does).

Reading around no-one seems to mention their ISC steps going much above 60 so at this point I'm still theorizing that the ISCV is maxing out and it still can't provide enough air under AC load. It would be ideal if there were some way to actuate the ISCV through software with the engine off (so I could pull it off with the harness plugged in and hit a button under actuators in Evoscan to move the ISCV in steps. Then I could see if it stops at 85 or is capable of more).

Thanks!

S.

Rom

Hi all,

Okay, I've confirmed that ISCV steps do exceed 85 under some circumstances (e.g. cold start).

However, the crazy part is that when AC turns on, it gets set to 85 and will not change no matter what the demand is! Revving the engine, or turning the steering, nothing changes it. It's like when it sees that AC is on, it just sets a fixed 85 steps. Demand still moves around as expected, but the actual steps don't change (like there is a lookup table somewhere just filled with "85" for all demands).

I've examined all the ISCV tables I can find and they all show that it should be much higher, but the ECU will not co-operate. The initial step tables with AC on are at 146, and I even tried raising it to 160. No changes.

Not sure if I'm missing a table.. Is there an ISCV lookup table with AC on??

This is driving me crazy so any help appreciated!

Thanks!

S.