Hey all, looking for some advice tuning my 89 K1500.
It's a 350 bored .020" with a 454 TB on a single pane holley intake, emissions delete. Also it's a 5 speed manual.

Cam specs are:
.458 lift intake and exhaust
218 duration @ .050" intake and exhaust
284 adv. duration intake and exhaust
110 lobe seperation

'7747 pcm, $42 mask, using winaldl for logging and tunerpro for the editing.

My issue is the idle seems to go up to around 2000 RPM whenever I push in on the clutch while driving. Once at a stop, the idle will gradually drop down to the desired idle. Watching the IAC counts, the IAC opens to near the max position when the throttle is used, then stays open for a while even after the throttle is closed. I suspected a sticky throttle at first, but the TPS% does drop to <10% when off the gas pedal.

I've found this thread: https://www.thirdgen.org/forums/diy-...-follower.html
I thought maybe this would be relevent, but honestly I don't know how to find 0x5E7 or 0x5E8, chalk it up to being a newb at this.
0x5E7: IAC extend delay, low vss (seconds / 5).
0x5E8: IAC extend delay, high vss (seconds / 5).

Delays IAC extend after an IAC retract command. Can cause a 'rpm hang' after a throttle blip or throttle lift.

So if there's anyone who's dealt with this or other idle issues that could help it would be very much appreciated.

 

Yep, they are the ones that cause the IAC to stay open for a bit. Only after max TF has been hit. The '7747 IAC control is dismal.

There is an IAC logic write up link in the Tuning Guide Book sticky.

Those address are the physical address within the PROM/BIN. Can use the hex editor in Tuner Pro to change them to 0.

RBob.

 

So go into the hex editor, and at 0000005E7 & 8 set those to 0. Right now they're 2 and 5. I'll see what happens.
I did end up finding the IAC logic in the sticky, not sure if it's the link I posted, but that sticky has been pretty useful.

 

Went for a short test drive with the dog, but not the laptop so no log. Definite improvement, idle comes down much faster and below 1500 rpm it doesn't feel like it's lugging.
Though it still revs up when coasting to a stop with the clutch in, or when changing gears. It does seem related to vehicle speed.

 

That is the correct thread that you posted. I had to open it to see that. What I do with stick shift cars is to work with the TF gain and the decay values. The gain I usually set for a max TF once 100% TPS is reached.

This is typically a lower gain and make it easier to drive the car.

Then the decays are set up so that the RPM falls to the proper speed for best shifting. Decay too slow and the RPM hangs high. Decay too quickly and need to bring them back up for a smooth shift.

Gain value:

0x5F1: Percent of throttle follower not in park/neutral (also manual)

Decays:

0x5E4: Low VSS filter coefficient.
0x5E5: Medium VSS filter coefficient.
0x5E6: High VSS filter coefficient.

RBob.

 

So with your ideal gain the IAC would only be fully open under tps 100% and just off idle would be slightly higher IAC counts than idle?

 

That sounds correct. I also allow a lot of TF steps as it is another source of air. Here are the current settings (see image). This is on an old school hot rod with a stick transmission, TBI.

RBob.

 

Should I be able to get to that stuff in the latest version of tunerpro? For this stuff I've just been going into the hex editor.

 

It's not TP RT version based, it's XDF based.

Another XDF for you application might (will) have a different amount of items defined.

At times I've had to use 3 or 4 different XDFs to get all of the parameters that I wanted. (I usually combine all paramaters into a single XDF though).

 

I'll have to keep an eye out for other xdf files but for now hex editing works fine. Changing gain from B0 to 90 has helped tremendously as the IAC counts are 80 while driving and 1600 RPM while shifting. Going to try it just a tad lower.

For decay coefficients is a lower value a faster decay or is that backwards?

 

Nevermind, drove it again and didn't change a thing. Not even when lowered. Some days I love tbi, some days I wish I went carb.

 

Backwards, a larger value is a faster decay.

The other thing to do is to adjust the idle stop screw so that the IAC steps are between 5 & 10. This is at idle on a warm engine with no other loads.

RBob.

 

I think everything is in the latest $42-1227747-V5.9.3.xdf including all you have been working on here. I've been working on this XDF for years! Can be found here:
http://www.gearhead-efi.com/Fuel-Inj...Information-42

Thank RBob for sharing all his work years ago!

I've been following all he has ever had to say on the subject and compiling it in this XDF along with some other work. May as well grab the ADX for TunerPro as well, it has data tracing, history tables and a whole bunch more!

 

Wow, that's a whole new animal! I'm excited to try it out! Maybe I can get datalogging working in tunerpro too. Lately I've been working with fuel and timing, hoping to get PE working decent once the more basic stuff is close. As far as my IAC tuning it seems just about right.Thanks for the help RBob, and of course EagleMark for sharing.

 

If you haven't read RBob's white papers on IAC control and another on Prop Gain do yourself a favor, Do That.

 

What is your fuel pump/injector size/fuel pressure? Not related to your reported issue. I am just inquisitive. I ran same ecu with similar engine specs for a few years.

 

Stock fuel pump, stock fuel pressure, injector part number was 5235231 which I believe flow 80 lb/hr. Recently moved my BPW up to 111 after I did some math and figured out some of my VE tables were adding to over 100. Tuning more of that stuff will be a challenge for another day though.

 

my error