devilfish

The rpms dont drop fast enough when I come from a cruise to a stop. I search about "T/F". And this came up:


Time between IAC steps in pk/Neu
L8659: FCB 8 ; 62.5 msec between stp's in Pk/Neut
reducing it will make the rpm drop faster

Time between IAC steps in Drive
L865A: FCB 8 ; 37.5 msec between stp's in Drive
reducing it will make the rpm drop faster

Slope gain
L865D: FCB 160 ; 150% follower slope gain
reducing it willl also get the idle down quicker, how?

MAX IAC steps in Drive
L865E: FCB 50 ; 50 steps max in drive
Max IAC steps in Drive reducing will allow the rpm drop off quickly (less steps to reduce).

Tables
IAC Manual throttle follower vs MPH
L86B2: FCB 0 ; 0 0 MPH
MAX IAC steps in Drive vs MPH reducing will allow the rpm drop off quickly (less steps to reduce).

I changed the 2 first tabels, no change.

I dont like to make random changes whitout knowing what im doing.
So has anyone got som exprince to change this behavior?
Next step is to take out some timing in overrun.
Iac steps in idle is 14.

thanks

gta324

https://www.thirdgen.org/techbb2/sho...ght=slope+gain

If you read it carefully it explains the most.......

/N.

devilfish

I noticed today that my car dont go back to idle while the car is moving?? When I put it in neutral the idle stays at 1100rpm. But when I brake to a complete stop, then it gos down to 750rpm, where I put it..

JPrevost

Interesting. I'd like to find that in the code. That just got me thinking about having a routine that knew what gear you are in (with a manual) and then with the vss it would match revs. Have a switch that turns off the feature... just thought that would be pretty neat to try out. I know the early throttle by wire stuff was obtrusive in a similar fashion. I felt like I was using a dial-up connection trying to drive. Floor the pedal and quickly lift and the engine doesn't even change a rev.... that was so not fun.

As for the TF's, I wouldn't really bother changing the decay rate except for the "idle". When driving around the decay rate is rather good (with a stock IAC) when you just limit the actual counts to a resonable number. I have mine set at 36 max and it works great because when I lift on the throttle to slow down I don't have to use the brakes but then it doesn't keep slowing down it kind of catchs the TF steps and the engine braking is less which I like at low speeds. A friends non-EFI camaro didn't even bother running vac advance and it was a beast to drive. The thing would engine brake so bad that you really wished it had shoulder belts even just driving at slow speeds .
The TF is there for 2 reasons; Emissions and prevent stalling. Since I'm not a huge emissions fan and my engine is tuned rather well, I just turn limit the TF which in the end makes me feel more in control. It's a preference thing. Also, if you've got a LOT of TF and really crappy brakes it can get scetchy. A couple years ago I pulled out into traffic (3 lanes) and a guy that I pulled out behind didn't indicate and stopped really short making me stand on my pedal... the engine was overpowering the brakes and it was scary. I think the RPM's were over 2000rpm and at that speed my mighty mouse is breathing rather substantially. So add that to another reason I don't like a lot of TF.

RBob

iTrader: (1)

Vehicle speed needs to be below this value:

L8495: FCB 45 ; 14 MPH MAX SPD FOR IDLE, MPH * 3.2

RBob.

{edit: nope, the above is for idle fueling parameters to be used. Looks like the idle control is hard-coded to zero MPH. This is the same as GM has done in other masks. Here is where it is done in $8D:

It is the LDAA L0083 with the BNE (Branch if not equal to zero, IOW, vehicle is moving)

RBob.
{/edit}

BronYrAur

iTrader: (1)

I've got an 8746 car with not too many changes to my LO3 and using a Prominator got the VE and spark pretty good, but it intermittently flares up the idle I've noticed and I'm almost sure its the IAC acting up.

It's a manual car, say I'm driving a certain speed and push the clutch in, the revs actually increase above what they were in gear. Sometimes, they go up then slowly go back down to normal, but other times it will rev up to like 2000 - 2500 when I'm barely moving. I can usually give it a little blip of the throttle and it will settle down.

Do you think this is caused from my VSS registering the wrong speed? (I swapped to 3.42's and didn't correct for it) has it not hit the minimum speed threshold for it to settle down? It's not good when i can just let it idle up like that and drop it into gear and it'll drive itself. Again, this is only intermittent, which makes me think it may also be mechanical, any advice?

Gary Anderson

iTrader: (2)

RBob,

So do we know what or where the idle speed is set to above 0 mph?

Regards,
Gary Anderson

devilfish

I tried to lower my "IAC Throttle Follower vs mph" from 10.00 to 0 in all cells, it helped. I did pick up low RPM "bucks" ( going from 0 tps to 1% and back ). How is that related?
But I whant the RPM to dropp even faster. What is and does the "IAC TF slope gain" ?

Thanks

RBob

iTrader: (1)

Sounds like a sticky throttle cable or TB shafts. The throttle blip correcting the problem is the give-away.

RBob.

RBob

iTrader: (1)

There is no idle state when the vehicle speed is greater then 0 MPH. So no idle speed control is being attempted.

RBob.

RBob

iTrader: (1)

Check a data log of when the bucking is happening. Good possibility the TF steps are switching in and out as the TPS% crosses the TF bias threshold.

The link gta324 posted above has a lot on the IAC TF slope gain. Basically it is the amount of TF IAC steps vs. TPS%.

RBob.

devilfish

Hmmm. Could you explain that a bit more? I dont quite follow you about TF bias threshold.
( that I suck at enligsh dont help either )

Cheers

BronYrAur

iTrader: (1)

Thanks RBob, I just kind of wanted to hear someone else say that too, so I knew it wasn't something being corrected in teh ECM.

RBob

iTrader: (1)

The TPS needs to be above a certain value for the TF to be active. If the throttle is just above that threshold then TF is active. Lift off the thottle just a little to below that threshold and now the TF is not active. This can cause sudden swings in TF steps.

The threshold is at L8647. However, before being checked against this threshold the actual TPS value gets modified based on several parameters.

RBob.

RBob

iTrader: (1)

One thing that can happen is that the throttle sticks open j-u-s-t enough that idle mode isn't entered. In this case increasing the TPS% threshold for idle can fix it. Such as using a 3% instead of 1.2% threshold.

RBob.

BronYrAur

iTrader: (1)

Ah very good idea, thanks a lot, Because I've already tried to resolve some issues with the TBI and don't feel like disassembling this Holley 670 right now.

JPrevost

The TPS sensor is very easy to adjust on the Holley TBI. Just loose up the 2 screws and twist or tap to make small adjustments.

BronYrAur

iTrader: (1)

Yeah it is pretty much right out in the open isn't it? I'll have to play around with that too, got plenty of time after tomorrow (end of finals week). Yet I still spend my time on here during finals

RBob

iTrader: (1)

This really isn't a case of physical TPS adjustment. The code adjusts itself to the lowest setting as the 'closed TPS value.' What happens is that the TB doesn't quite close, with the result being no idle speed control. The TPS% is open just a hair too much. It only takes 1/3 of a percent too far open to bypass idle speed control.

RBob.

BronYrAur

iTrader: (1)

Ah there's the light bulb going on in my head. I forgot about it setting closed TPS wherever it's at. Looks like the threshold is at about 1.9% in my .bin, I'll try it out at about 3%, thanks a lot.

devilfish

Update.

2 main things where changed today that helped me ( not entirely fixed ) my idle to hang for a long time during deaccel..

I used to little timing at idle, when I bumped up the timing the idle got more stabel and it seems like the IAC dident have to compensate as much to keep it "alive". I dunno but it helped me. I used to run 20, but my hotcam really like my new setting at 27..
After this I made a new "minial idel-set", aswell as VE changes.

Then I decreased the "gain slope", from 125% to 80%.

Now im pretty happy with the result. Will make som new runs to se how it works, then perhaps lower the gainslope even more.

Cheers.