brennanw

Newbie here, so please bare with me.

I'm trying to get my 383 TBI tuned and I'm having some trouble getting the idle to come down. It starts up fine, warms up and then falls down to about 100 RPM shy of my target idle of 700 RPMs. At this point the idle tends to fluctuate slightly (800-900 RPMs). Now, if I shut off the engine and start it back up, it idles very smoothly at 700 RPMs. Any ideas as to what might be causing this?

Grumpy

Hook up your scanner and closely, real closely look at what your IAC counts are doing.

And make sure you min idle is set right.

RBob

iTrader: (1)

Seems like the idle just floats high? BTDT. However, it can be fixed. Couple of things to check right off.

Does the throttle return back against the idle stop screw? Sometimes after a while the throttle shaft bores get worn, or the throttle cable sticks a little. It can help to increase this term:
1% is a little low, I like 2.5% to 3% (2.5% / .39 = 6) if the throttle hangs a bit.

Make sure the VSS is reporting 0 MPH when stopped. No idle control unless at 0.0 MPH.

If the engine thermostat temperature rating has been reduced, or the engine just likes to run cool, then the steps in this table may need to be changed:
The steps in the temperature range of the normal engine operating temperature need to be less then the kickdown steps found here:
RBob.

brennanw

This is it precisely. My IAC steps hang at about 85 but if I retart they immediately come down to about 45. I need to have about 45 to get the idle smooth at 700 RPM. Any idea why the IAC is hanging at 85? (Note: I only get the IAC "hang" when warming the engine up from a cold start.)

brennanw

Whoe, RBob. When you start putting hex in front of me I start to get a little queesy. Remember that I am a newbie, I use TunerCat

Originally posted by RBob
"Seems like the idle just floats high?"

Yes, it does.

"Does the throttle return back against the idle stop screw? "

Yep, I made sure of that by adding some extra return springs.

"Sometimes after a while the throttle shaft bores get worn, or the throttle cable sticks a little."

I just had mine re-bushed so I don't think this is the problem. And my throttle cable moves very freely.

"It can help to increase this term:
1% is a little low, I like 2.5% to 3% (2.5% / .39 = 6) if the throttle hangs a bit."

Uhhh, what would this be in TunerCat language?

"Make sure the VSS is reporting 0 MPH when stopped. No idle control unless at 0.0 MPH."

I'm not using a VSS so I think I'm OK with this one.

"If the engine thermostat temperature rating has been reduced, or the engine just likes to run cool, then the steps in this table may need to be changed:
"

I thought that this table was only used during open loop warm up? Doesn't this table time out or stop being used once the ECM goes into closed loop?


"The steps in the temperature range of the normal engine operating temperature need to be less then the kickdown steps found here:
"

And the TunerCat traslation to this is???


RBob.

brennanw

Why? What does "KICK DN ADJ STEPS" represent? Does this have anything to do with an automatic trans? I'm using a manual, does that make any difference here?

RBob

iTrader: (1)

I can't help with the Tunercat representation of the above terms.

As for the KICK DN ADJ STEPS, it is the key for the ECM being able to go into a closed loop idle. Until the steps in the IAC MOTOR POSIT vs COOLANT table are less then the kickdown steps the ECM will not go into a closed loop idle. As the engine warms up the row in use of the IAC MOTOR POSIT vs COOLANT tables changes with it.

RBob.

brennanw

Ok, that makes sense. The "KICK DN ADJ STEPS" is just simply a limit that must be met before CL can be enabled. The name is somewhat confusing. If I understand this correctly, I could disable CL by setting this term to 0 and leave my IAC steps >0, right? I have a copy of an ASDZ hac but I don't know how to read it yet, so please excuse my stupid questions.

RBob

iTrader: (1)

As for your last question "I could disable CL by setting this term to 0 and leave my IAC steps >0, right? ", yes, it would disable closed loop idle control.

The term "KICK DN ADJ STEPS" is really also what it says. After a certain time period the IAC will be reduced by those amount of steps. The time period is typically a few seconds after engine run. The kicker is (ooohh, bad pun), is that GM decided to attach closed loop idle to the number of kick down steps vs. the IAC position vs. coolant table values.

You have no idea how long this took to figure out. Some people still don't believe me when I tell them how it works. It is the dual functionality of a single term tied with the dual functionality of another table that makes it work the way it does.

RBob.

brennanw

Very interesting. I'm particulary interested in the logic going on here "GM decided to attach closed loop idle to the number of kick down steps vs. the IAC position vs. coolant table values." I assume that this should become evident when I study the hac.

brennanw

Well, thanks to RBob I just about have this one solved. In this thread RBob explained that Pin B10 should be left open when running a manual trans. This really made a big difference with my idle when bringing it up to temp from a cold start. But now I have a new observation that I think is purely a ECM logic problem and not a hardware problem.

Let me restate the facts:

Before:
Cold start to warm idle = idle surge (800-900RPM range)

Now:
Cold start to warm idle AND warm start = great idle at 700 RPM with no surging until...

The Problem:
However, if I rev the engine up a bit in neutral to ~1500-2000 RPM the idle will fall back down to ~700 RPM and then immediately start surging from ~600-800 RPM. The only way I can get the surging to stop is if I kill the engine and restart. In addition, if I slowly bring up the RPM (while still in neutral) from ~700 to ~2500 the surging will continue throughout the entire RPM range.

Any ideas?

Low C1500

Try playing around with your prop gains at idle, also your AE vs. map might be too high at low delta map. Your motor could be adding too much AE all by itself when the rpms are increasing as the ECM hunts for the idle rpm. I'm pretty sure that the 747 uses AE map at closed idle. Maybe someone else can shed some light on this.

brennanw

I've been told that I shouldn't even try to tune AE until I get spark and VE tuned. I've been doing a lot of searching and I have found that surging is very common on TBIs and that there are many different causes. However, my surge has one important difference that none of the other surging threads have...my surge does not present itself until after I move the TPS. If I never touch the TPS, the idle would stay perfectly smooth. I checked the TPS values and I didn't find any dead spots. It also returns back to the same value after moving the TPS lever. So this makes me think that it's a logic problem in the code.

RBob

iTrader: (1)

Surging can be tough to figure out. Usually it is a spark and/or VE thing. You mentioned moving the TPS, that by definition means moving the throttle blades. This causes a different area of the tables to be used, RPM goes up, MAP goes down. As the '747 ALDL is too slow to use in an instance such as this, it may take just some playing with the tables.

An upward surge is typically caused by either/and the fueling going lean, SA being added.

RBob.

Edit: by 'moving the TPS' are you doing this under the hood by hand w/o moving the actual throttle? If so, make sure that when you do this the injectors spray more fuel as it is moved in the same direction as an opening throttle would.

brennanw

I've done both. I have moved just the TPS and I have moved the TPS by moving the throttle. In either case more fuel is sprayed.

I replaced the TPS today with a brand new one. I didn't think it was the problem but I am desperate. Sure enough, the surge is still there. Would one of you generous gents take a look at the attached BIN and tell me what you think? I'll also attach the latest WinALDL log file. Rename the file extension on this post to *.bin after you download it.

Ok, that didn't work. The site won't let me attach the file. Well, if one of you would like to take a gander at these files, send me an email and I send you the files.

brennanw

Alright here's some links to the files.


BIN


Log File

Ronny

iTrader: (1)

i have the same problem. i have been studying these posts to get some understanding. for a while i thought is was due to my throttle cable hanging up. if i stabbed the throttle at idle it would settle down and idle nicely 700 rpms. manual trans. if i drove to next stop sign would idle high. tickle throttle settles down. occasionally surges not always. turn on AC and that seemed to help reduce idle but never died. one of my two IAC's not moving as defective. i read a post to set commanded idle in prom (tunercat) to a lesser fiqure then adjust idle on stop screw to about 50 rpms higher. this may remove the ecus ability to correct idle? not sure if i understand this ploy? also it was said at idle it is bouncing around cells from one to another as idle moves around on rpm. each cell has diff VE and also a diff spark. this too is like a cat chasing its tail. moves to one adjusts, then moves to another and wants some thing else and adjusts. i will be look at all that in spring when weather allows driving. however throwing in other issues as cam swap and 454 TB install.

Grumpy

How about reposting the log with terms that make sense to other then a gifted few

Atta glance it's hard to tell what you idle K/Pa region is.
IAC counts for park position seem a tad high.

Might try reading thru a hac and seeing exactly what IAC tables/limits there are.

brennanw

Sorry about that. It's a WinALDL tab delimited log file. Here it is in Excel format.

Log File

The idle MAP is about 42-43 KPa. I've been looking at the hac but I don't understand it all just yet. I'm still trying to make sense of the instruction set for the 68HC11.