Hi all,

I was doing some logging today, and I was looking at the sensor data, and the IAC was counting down, all the way to 0.

I had never seen that. So I was thinking about it and since the IAC allows air to come in, is it possible I have a vaccum leak and it's causing this?

Any input would be greatly appriciated. thanks

 

Not necessarily, could just be the TB stop is adjusted more open, this zero IAC counts at hot idle, helps to reduce surging.

What is the target rpm vs actual?

 

Forgive my ignorance but where would I find the Target RPM? I'm using the ASDU bin, if that helps.

 

I believe it is a coolant based table. Should be in tunerpro "tables".

 

Idle RPM vs Coolant Temp in Tuner Pro.
6E in the tables.
Had to adjust mine 3 times before settling in at my
target 950 at 180.

HTH

Later

 

Ok, I think I found it under "Desired C/L Idle Speed"

C RPM
115 650.00
110 625.00
105 575.00
100 525.00
95 525.00
85 525.00
75 575.00
65 600.00
55 600.00

 

That looks like it.
What XDF are you using and what version of Tuner Pro
are you using.

That might be the wording difference.


Later

 

4.14!
and 42.XDF 1.110000

 

The latest version is 4.14.0381.

Didn't say what application were talking about.
Not familiar with that XFD.
Shows 87-91 5.0 Truck. Correct??
What Bin??

Later

 

On your scanner/datalog it may be listed as desired idle rpm.

Don't jump to changing tables just yet, you can, but it is better to get the "I want this idle" to match the "I got this idle" first. Then see, if it is what you really need or want.

If you ever, later on, fix the idle "offset" (desired vs actual) then your tables will need to be corrected also.

Just remember EVERYBODY is dumb at SOMETHING.

Brain surgeons don't always know how to plant potatoes, so if you are ever hungry don't ask, you will starve by the time they figure it out, if ever.

 

Jaykar, its actualy a 5.7 truck.

Pandin, I found it up above #6 and it was desire c/l idle speed.

 

How does your desired cl idle speed compare to the actual idle speed when you data log or scan it?

 

actual idle is between 600-650

 

And what is the targeted/desired idle at the 600-650 spot???

I check mine in park and in gear @ 0 mph (auto). The desired is set in the table at 575, in park it adds 50 rpm, so it idles at 625-650. When in gear (0 mph) the idle will drop to 550-575.

If your engine is idling below the desired idle, IAC steps should be added.
If above, IAC steps removed. If your IAC steps/counts are at 0 @ warmed up idle, and your desired idle matches your actual idle. There is nothing "wrong".

If you want to see some IAC steps/counts, back off the idle stop screw on the Throttle body, a 1/4 turn should work and the IAC should start to raise a few steps/counts. If not try another 1/4 turn. If this is were you are going to leave it, be sure to reset the TPS min volts if needed.

You can also watch the IAC numbers as it warms up in idle. If the desired idle speed continues to drop after the IAC hits "0" then the blades are open a bit too much. Close the blades and raise the table to the idle you want.

 

I hope this is not a thread hijack,; it is a related question...

Exactly when and under what circumstances does the IAC open and close?

I have been having problems where coming off a hard accel, push in the clutch and my idle will be over 2000 rpm. I can roll to a stop and idle will s-l-o-w-l-y come back down. It seems like the IAC is opening up and then eventually deciding to close back down to idle.

Regardless of throttle position sensor output, I would have thought that the IAC only moved during idle (and cold start).

I am working on getting data logging hardware/software, but have not achieved it yet, so I am still seat-of-the-pants troubleshooting! Any advice is appreciated.

 

What you need to look at is the throttle follower (software setting), and yes the IAC is used (moves) all the time.

 

Fyrebird: I believe there is a decay value to the IAC routine. If fact there may be a couple. I honestly dont know which way to move it but change it a bit and see effect.

IAC is used on cold start, cold coolant, throttle follower, PE, and others. I currently am not using my IAC(??) and find that on brisk deacceration the manifold is stripped of all fuel and serious enleanment occurs which can produce a stall at stop sign or slowing to round a turn and then accellerating a bog sometimes occurs.

 

I lowered mine from 5 to 4. "IAC Steps Added to T/F in Drive"

T/F = throttle follower

 

So the IAC opens and closes while following throttle position?

I didn't know that this value could be changed. (This is a 1986 ECM.)

More info - the problem (IAC holding idle too high) seems to be less noticeable on a warm engine.

 

Somebody can give the exact location, if we know which bin you are using.

If your cold idle speed is high, there is the "Idle RPM vs Coolant Temperature" that can be adjusted.

Where the TPS at idle is adjusted, relates to this issue, at less then 20 IAC counts, rpm hang can be worse.

 

[quote=pandin;3912223]Somebody can give the exact location, if we know which bin you are using.

If your cold idle speed is high, there is the "Idle RPM vs Coolant Temperature" that can be adjusted.quote]

Does that mean burning a new PROM? I didn't know that parameters were otherwise editable.

 

If you are really smart, you could reprogram the chip and use the ECM/Eprom to run a washing machine or a pop machine. Assembly language knowledge would be required.

 

As the original poster commented "vacuum leak" has to be ruled out.

 

I replaced all the vacuum lines when I first started chasing this problem. Also checked the intake bolts. Any other areas I should look at for vacuum leaks?

 

I am not much of a mechanic. But when we added the manifold and 7.4L TBI I noticed that the TBI base gasket did not match the bottom of my TBI. I found a diff as I had a later 1995-1996 unit. The gasket has to cover the IAC passage if not a huge vac leak.

 

I believe the IAC movement and added fuel along with follows the TPS changes. With or without AE event. If the TPS change is significant I think the AE then triggers. so subtle changes in TPS with no AE there should be IAC step changes. I think throttle follower refers to the added fuel as IAC moves(open).

 

Youl lost me - what's AE?

 

acceleration enrichment. AKA pumpshot

 

The Throttle Follower also keeps the engine rpm up, to match the road speed (coasting at low speed), this improves drivability, as the engine doesn't, up and down in rpm, as you up and down the gas pedal.

 

That accurately describes what I'm seeing, except the lag time for the IAC to catch up is exceedingly long. I'm talking 20-30 seconds.

 

what pandin said. also with a manual trans nice to hold a higher rpm when moving through the gears. if too high however aggrevating. like too much of a good thing.

 

In addition to a vacuum leak and leaky or loose base gasket, another source of extra air is worn throttle blade holes. When worn these both allow extra air in through the enlarged holes and also keep the throttle blades from seating properly.

Check them by seeing how much side slop you have on the throttle shaft by pushing it back and forth.

Paul T.