Guest

OK, got a memcal from Jason, working fine except I can't get the IAC counts down to 40. Set the timing to around 6 BTDC, set idle on 383 to 580 RPM and got about 16 in.hg. but can not get the counts down no matter what I do.

Here's the Autoxray file;

101 >>>>>>>>>> Vehicle Scan Report <<<<<<<<<<
Trouble Codes No Trouble Codes Found Vehicle Data
PROM ID 5801
Coolant Temp 181.4°F
Start Up Coolant Temp 161.1°F
Throttle Sensor 0.52 Volts
Throttle Angle 0%
Engine RPM 947
Vehicle Speed 0 MPH
Oxygen Sensor 700 mVolts
O2 Cross Counts 105
Block Learn 122
BLK LRN Cell 4
Integrator 133
Idle Air Mtr Pos 160 steps
Desired Idle 950 RPM
MAP Sensor 2.46 Volts
Manifold Air Tmp 68.0°F
EGR Duty Cycle 0.0%
CCP Duty Cycle 0.0%
Battery Voltage 12.0 Volts
Fuel Pump Sense 12.1 volts
Learned Idle Pos 40 steps
Oil Temp -38.6°F
Spark Advance 21.3°
Knock Sensor 2
Knock Retard 0°
Injector Pulse 2.5 mS
Engine Run Time 307 seconds A/C
Not Requested A/C Forced Off No
Battery Voltage High : No
Shift Light Off
TCC Status Not Locked
Park/Neutral Not Detected
Fan Number 1 On
A/C Clutch Disabled
Oxygen Sensor Ready
Fuel Cut Off Disabled
CCP Purge Off
Air Divert Solenoid On
Air Switch Solenoid Off
Learn Control Enabled
Rich Lean Flag Rich
Loop Status Closed
Capture Data

I have onboard A/F ratio, it's say slight rich most of the time.

I've isolated all vacuum taps and checked PCV.

Have went through the setup procedure for IAC and TPS multiple times and it still goes high counts.

It doesn't seem to be running too bad, a plug visual check did not show fouling problems.

Have swapped the IAC motor out and no change.

Could I have a vacuum leak? I have to admit it was very tough getting the timing down to 6 BTDC without dying.

I've checked the IAC motor resistance it's OK.

The wiring between the 7730 and IAC is correct.

Anyone got and idea of whats happening?

Thanks.

GS #883

Mark,
This may be beyond me, but I will give it a shot since you haven't gotten any replies.
When I changed my cam, and had heads/intake ported, etc., my IAC went to about 80. My desired idle was raised during the performance changes via computer, from 700 to 900. Anyway, I was getting some surge at idle and I knew that the IAC should be closer to 30-40 counts. I increased the throttle position at idle (opened the blades more), and the IAC went down from 80 to 30.
I understand the theory is that the IAC adds air "around" the throttle body, if the throttle body isn't providing enough air. Again, maybe you know the above cold; and I am not trying to insult your knowledge, but if you haven't tried to open the throttle blades more, it may be worth a try. I realize you have a 84, and maybe the above doesn't apply. If so, please disregard. It looks like your desired idle and actual are about 950. How do you "set" the idle down to 580 rpm???

Also, any help from the guys that may have advised you on the setup. In my case, that was Ed Wright, and he gave me awesome computer related support, before and after the sale.
Good Luck

olephart

[quote] It looks like your desired idle and actual are about 950. How do you "set" the idle down to 580 rpm??? [quote]

That's my question too. Maybe its different on L98's, but "desired idle" is from the computer - that's what is "set". Since it's ideling at real close to that, you don't have a problem. I guess you would have to reprogram if you want a lower rpm.

The IAC will read higher (LT1) as rpm increases. As long as you are ideling smothly at the desired rpm, it really does not matter.

Hope I am understanding your post.

Guest

Thanks for the comments, the idle is with IAC in.

I have since set base idle at 580 or so and had IAC control at a lower RPM, say 800, as you know, bigger stroke will require a higher idle RPM. If I try to open the TB up more, it fights the IAC and starts surging. This is what is so puzzling. I had a thought that maybe I was adjusting down my idle to compensate for a vacuum leak and the IAC was trying to lean out the A/F ratio by going to 160 counts. My vacuum is not rock steady but it only varies by say 1 in.hg. unless I open up the throttle blades too much and fight the IAC. It's almost as if I'm not getting a good counts reading from the ECM.

I've had the Holley off and checked for anything that might bypass air around the blades, nothing. They are very slightly cracked at idle, barely noticable, maybe someone can tell me how much they are open on their car at idle

As far as 84, the only thing that remains 84 is the cosmetics, basically, I'm running a 90 Camaro setup with 7730.

Thanks for chiming. :chevy

MJ

I had symptoms like yours. My autotap said the IAC request was at 160 but my RPMs weren't coming up. Drove me nuts for a while till I realized that I was reading what the PCM (96) was asking, not what the IAC was doing. I tested the IAC and it checked out. But, I had a spare IAC so I swaped it out. It fixed me right up.

JAKE

You need to set your minimum idle speed setting to about 100 rpm below the command idle speed that's burned into the PROM. This will cause your IAC counts to drop.

If your TPS is adjustable, you'll also need to reset the voltage once you get your IAC counts to where you want them.

There's a special procedure for resetting the IAC once all that's done so that the ECM has a new base to reference. I think you know it though, since you said you've reset it already.


Hope this helps.

Jake





[Modified by JAKE, 1:31 PM 3/11/2002]

Guest

OK, here's another scan. The IAC is down to 48 counts but idle is too high, must be my chip programmed idle? The vacuum is at 17 in.hg with this scan and steady as a rock. I slowly added vacuum taps, air divert, EGR, Purge Can, nothing brought the vacuum down so I must be dealing with something on the memcal.

Yeah Jake, I set my idle without IAC to 580 but don't know exactly what Jason set my idle on the memcal. He must be out of town or something.

101 >>>>>>>>>> Vehicle Scan Report <<<<<<<<<< Trouble Codes No Trouble Codes Found
Vehicle Data PROM ID 5801
Coolant Temp 189.5°F
Start Up Coolant Temp 58.5°F
Throttle Sensor 0.58 Volts
Throttle Angle 0%
Engine RPM 909
Vehicle Speed 0 MPH
Oxygen Sensor 696 mVolts
O2 Cross Counts 167
Block Learn 126
BLK LRN Cell 4
Integrator 126
Idle Air Mtr Pos 48 steps
Desired Idle 912 RPM
MAP Sensor 2.62 Volts
Manifold Air Tmp 64.4°F
EGR Duty Cycle 0.0%
CCP Duty Cycle 0.0%
Battery Voltage 12.1 Volts
Fuel Pump Sense 12.2 volts
Learned Idle Pos 40 steps
Oil Temp -38.6°F
Spark Advance 26.2°
Knock Sensor 9
Knock Retard 0°
Injector Pulse 2.7 mS
Engine Run Time 1197 seconds
A/C Not Requested
A/C Forced Off No
Battery Voltage High : No
Shift Light Off
TCC Status Not Locked
Park/Neutral Not Detected
Fan Number 1 On
A/C Clutch Disabled
Oxygen Sensor Ready
Fuel Cut Off Disabled
CCP Purge Off
Air Divert Solenoid On
Air Switch Solenoid Off
Learn Control Enabled
Rich Lean Flag Rich
Loop Status Closed
Capture Data

This is with 45 psi Fuel Press set with vacuum disconnected (I'm running FMS #24 Inj). The A/F indication off my onboard gage indicates slightly rich.

Do you guys see a problem other than maybe memcal RPM setpoint?

Thanks for the help!

Mark

olephart

I still don't understand what you are doing to "set" the idle to 580 rpm. The desired idle is programmed into the computer. Your trace indicates that it is doing exactly what it is set to do. If it's not rough or missing, then it seems to be fine. If you want it to idle lower, set the value you want in the computer.

Still not sure I am understanding your questions.

P.S. 12.1 volts is low, but may be because of idle speed. Make sure you are getting 13+ at 1,200 and up. If not, you may have a battery or charging issue.

Guest

olephart,

I'm disconnecting the IAC and setting base idle to 580 so that IAC will take the lead in controlling idle once reconnected and not fight the throttle body for idle. BTW, 580 is about all I could get it down to and still run.

Someone is doing my chip burning so I'll have to get with him, just wanted to make sure it wasn't something other than memcal programming. "Desired idle" changes on my scans, it never stays the same, if I change idle setting it changes. Is this not normal?

I'll check the volts, I may not have enough alternator now after my buildup.

Thanks for the input.

PeteL

Desired idle is basically what has been programmed into the chip, and it's doing it's job by keeping you around 900 RPM as requested. It changes based upon load and perhaps other factors in the programming such as AC request.

So to get it down, you will need to reprogram.

Just a question, when you set the min air adjustment, are you putting the ecm into diagnostic mode?

Pete

CFI-EFI

Here's a shot in the dark from a guy that doesn't know "JACK" about, computers, programing, or diagnostic read outs. You have the vacuum disconnected from the FMU. If it were connected, your fuel pressure would be lower. My theory (shot in the dark) is that since you have observed it running rich, the ECU is adding air to correct the mixture. Because of the amount of air required to do this is excessive, the idle and IAC counts are high. Try hooking up the vacuum to the FMU and limiting any other sources of excess fuel, and see if that doesn't help. Probably not, but that's the best this dummy has to offer. Good Luck!

Guest

Yes, jumper ALDL a to b, turn on key, wait 1 min, pull IAC connector, turn off key, pull jumper, restart and set base idle at TB to lowest possible RPM, turn off key, check TPS voltage, reconnect IAC, restart, check idle, scan, etc.

I'll check with Jason on changing idle setpoint. Thanks PeteL

olephart

PeteL said what I believe is correct. My limited knowledge is with LT1s. The butterfly in the TB is closed at idle and the IAC allows the proper amount of air to make it idle at the "desired" speed. The IAC and TB are not fighting.

The IAC number is an indication of how open it is. 40 is a nominal figure for a stock engine in good shape. Mine was 60-70 when there was some carbon buildup restricting air flow. I suspect that a larger engine would need more flow at idle and the IAC readings would be higher.

If the IAC can not open enough to idle properly, some people drill a small hole in the butterfly. This lets enough air in for the IAC to modulate within it's range. It is not clear that you have this problem since the car is running fine.

I think Jason will clear all of this up when you get in touch with him.

Sorry if the LT1 info is not the same as L98 - just trying to help.

Guest

Thanks buddy, good info. Thanks all!

HighHopes85

I play around with my idle settings a lot so this comes from experience and not necessarily what is right or wrong. Take it with a grain of salt.

You have a couple of different parameters that control idle. The main one we think about is like the fast idle cam on a choked-carb. You start off high and as the choke opens, the position of the fast idle screw tends to wander onto another step of the fast idle cam. In your MAP car, the majority of this is controlled by the main idle RPM vs Coolant table.

Then there is what I call a throttle kicker on a carb. It is a solenoid that actuates under certain conditions like when the AC is commanded on. There is a table in the PROM that correlates to this. It adds a certain number of RPM when the AC (or defrost) HVAC control is selected. Stock PROMs usually have this set fairly low (from what I have seen, about 15-30 RPMs).

There is also an add to idle in park/neutral. This table generally helps me out only when tuning, so I can keep it kinda high in case I feel like she is going to stall in gear. You don't want this too far off from the main table or you will be doing the equivalent of a neutral drop every time you shift from park to neutral.

So what it all comes together as: main idle RPM + AC commanded RPM + Add RPM in P/N = Final 'desired' idle speed.

When I tune idle, I will not do the IAC reset to start off with. I merely look at the IAC counts and try to adjust them so they are around 25 in park. I do this by using the TB adjusting screw. Once I have this, I reset my TPS and finally reset my IAC using the usual jumper method.

After I am all happy that things look great, I have the scanner hooked up and put it into drive. First, I make sure she doesn't die ;) Then I make sure that my IAC never goes below 10 since I want to keep it active. The lowest idle I will ever need is based on the main table at the warmest engine temperature and in drive without AC. So that is the point I aim for when attempting IAC counts of ~10.

I can not set my minimum air rate as called for in the tech tips because I have modified the idle tables in the PROM. Once those tables have been modified, the best shot is aiming for 100RPM lower than the lowest idle your vehicle should ever experience (like mentioned above).

Looking at the desired idle RPM on the scan data, I would say that you have a high idle programmed in (you already know that ;) ). Either it comes down in the chip or you get a second charge card from the gas station :D And BTW, 17 in-Hg of vacuum at idle with a 383 is :cool:

Good luck, -Matt-

65Z01

Mark84_L383, you are using the proper procedure for setup.

The idea is that you fully extend the IAC pintel so that all air comes past the throttle plates; then adjust the base idle by positioning the plates with the set screw (~450rpm for a stock L98).

Then the TPS is set to .52Vdc at the base idle position.

This is the baseline for the ECM to use in achieving the desired idle setpoint using the IAC

BTW, note that "desired idle" is also a function of throttle position (i.e. TPS reading). Verify this by opening the throttle position a little, run a scan and see if the new "desired idle" isn't higher than at idle.

95Aqua

OK, here's my 2 cents. Been doing a lot of reading on this and if I find the link I will post it. But basically, what I've read is that on the aftermarket TB's there is a hole missing in the IAC circuit that is in the factory TB. Check the picture. Don't know the size, you need to get it from your original TB. But this hole needs to be there especially for bigger cams. Opening the TB blades won't cut it because the bigger cam causes reversion in the intake and causes baddly split BLMs at idle. So, you want the blades as closed as possible and use the IAC to control idle air. To do this and keep IAC down you have to drill this hole.

Also, there is another problem with some aftermarket TB's, namely BBKs, not sure about the Holley 58. I have a Holley 52 and don't have this problem, but anyway. The problem is that the IAC circuit needs to be isolated and on the BBK there are two notches that lead from the TB blade openings to the IAC. These need to be blocked off.

Again, if I find the link I will post it. Hope this helps...



Found it. There is lots of good programming stuff on this page, plus his car is really cool! http://para.noid.org/~lj/
[Modified by 95Aqua, 10:58 AM 3/13/2002]


[Modified by 95Aqua, 10:59 AM 3/13/2002]


[Modified by 95Aqua, 11:00 AM 3/13/2002]


[Modified by 95Aqua, 1:39 PM 3/13/2002]

Ramrod92

This would have me wondering... (Oil Temp -38.6°F)
:confused: