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Old 08-05-2022, 09:44 PM   #26
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Re: High idle on each start

The system will also add to the amount of fuel injected when it compensates for low voltage.

The coolant temp looks very good in that data set.

The oxygen sensor is swinging well and that will most likely even be better when the problems are taken care of.

The amount of fuel injected is closer to normal compared to the earlier data.

It is not expected to see a good IAC count at this time.

Get the voltage issue fixed and I bet everything else will move into place.
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Old 08-10-2022, 09:27 PM   #27
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Re: High idle on each start

At what temp is the ecm supposed to switch from closed loop to open loop? 195?
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Old 08-10-2022, 10:26 PM   #28
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Re: High idle on each start

Quote:
Originally Posted by Boog View Post
At what temp is the ecm supposed to switch from closed loop to open loop? 195?
My guess is you will not be able to find exact criteria on this.

It takes three things to get to closed loop:
A certain amount of time must pass
The coolant temperature must be “warm”
The oxygen sensor must be warm enough to generate a working signal for the ECM

I have training manuals from General Motors which were used and the GM training Centers and I don't think they even have this criteria anywhere in them.
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Old 08-12-2022, 08:58 PM   #29
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Re: High idle on each start

I did put on a new alternator and that raised the voltage to 13.7 to 13.9. The engine still ran the same.
The cable does have the 10k resistor and is necessary for data flow on this vehicle. If I switch it off there's no data.
Also, that resistor will cause idle speed increase and timing increase as stated by the supplier Red Devil. That explains the wild swing of rpm when moving from drive to park as it doesn't do that when the cable is not hooked up.
Today I swapped the prom with that used one I picked up and it made no difference.
The fan clutch is a Delco unit a few months old and the thermostat is a 195* also a few months old.
I paid attention to the engine temp and the point at which the fan clutch engaged and that is approximately 190*. I covered the grille in an attempt to raise the engine temp but it held steady at 190 all while idling in park for 20 minutes. There are times when the temp did reach 198 but not today.
I removed and opened the ECM to inspect it and it looked like new inside. I examined the board and found no burn spots or weak solder issues. The plug terminals are all clean. I'm a mechanical guy. If I can see what's broken, I can fix it. I am weak on electricals. I don't know how to effectively test an ECM.
I checked to see if the case needed to be grounded and there is no voltage escaping through the case. I did notice the ECM got awfully hot though, almost too hot to hold onto. That may be nothing.
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Old 08-12-2022, 10:02 PM   #30
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Re: High idle on each start

I am ok with it running at 190 degrees. The system has thresholds in the mid 180s that it made it through.

If the 10K has to be in place to see data, then it won't work for further diagnosis on the idle problem you are having. It was not a waste. It ruled out several things and found the low voltage problem.

The only other thing I want to do is to see data without the 10K resistor in place. It sounds like WinALDL can't do that for your truck. Almost all my experience is using that equipment the dealer owned which was the Tech 1, Tech2, OTC, CAMS, and the earlier equipment that I don't even remember what it was called. Everything has been taken care of that I can think of that is external of the ECM.

After the new alternator did you take it for a drive over 45 MPH to get a relearn without the WinALDL connected?
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Old 08-12-2022, 11:23 PM   #31
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Re: High idle on each start

Quote:
Originally Posted by ChevyTech View Post
I am ok with it running at 190 degrees. The system has thresholds in the mid 180s that it made it through.

If the 10K has to be in place to see data, then it won't work for further diagnosis on the idle problem you are having. It was not a waste. It ruled out several things and found the low voltage problem.


After the new alternator did you take it for a drive over 45 MPH to get a relearn without the WinALDL connected?
Yes. I replaced the alternator last saturday and drove it most everyday since.
I have not replaced the Map and it should be the original. I tested it months ago to be sure it holds vacuum. Map and ECM are the only things left that haven't been replaced, electronic wise. The rest of the engine electronics are all new including the distributor. Some of that was intentional though due only to the age of the truck.
Thank you very much CT. Your knowledge and experience are greatly appreciated.
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Old 08-13-2022, 07:44 AM   #32
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Re: High idle on each start

You're welcome.

There is a deceleration mode that holds the IAC open a little like a dash-pot on a carburetor. I believe the RPM, TPS and MAP signal are used for the ECM to decide when to bring the RPM down to regular idle.

The 0.9 volt reading in the data is a little off from what I would expect to see. I think the the spec GM puts out is 1 to 2 volts at idles. 0.9 volt could be out of the range it wants to see. The system could think the truck is decelerating.

Here is something you can try with the MAP sensor. When it is idling to fast, with a warm engine, bleed off some of the vacuum to the MAP sensor by holding the hose partially on the port so the vacuum is lower to the MAP and see how the system reacts.

The MAP sensor is interchangeable for many vehicles. Think of it as a electronic vacuum gauge. You could try swapping a MAP from another vehicle for a test.
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Old 08-18-2022, 05:56 PM   #33
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Re: High idle on each start

CT
I tried easing the hose off the map and it immediately tried to die as I'd expect with a big vacuum leak. Even pinching it off it stumbled and died.
Last week I reset the minimum idle speed which opened the throttle blades a smidge (any less and the throttle blades stick closed) and changed the tps reading. I wasn't happy with the tps reading being off. Since the tps has no adjustment, I had to slot the two holes to turn it back into spec. It is at .47 volts now at idle instead of .67. It rolls smoothly to 4.44 volts and back.
Upon warm startup with AC off it still climbed to 1025 rpm but I put it in drive then back to park and it settled at 700-750 so I then began logging to see how it all reads at that lower rpm.
The IAC stays at 0 until rpm revs to near 1000. I unplugged the iac a couple of times while it was running but it made no changes to the engine or the 0 reading. No CEL either. It ran the same.
On one log I revved it up to 1500+ for a bit to observe readings at that point.
While I don't understand all the readings, nothing jumps out, to me.
I guess I ought to test the Map voltage again. I don't have another vehicle with that type sensor to compare to.
Attached Files
File Type: txt 20220818_151438_LOG.txt (3.2 KB, 15 views)
File Type: txt 20220818_151249_LOG.txt (1.2 KB, 15 views)
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Old 08-18-2022, 08:02 PM   #34
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Re: High idle on each start

The top link has the system running in open loop. The TPS reading is bad.

The bottom link has the IAC at zero which you never want to happen. The throttle stop screw is holding the throttle to far open. The TPS reading is bad. It is in closed loop operation.

Well at least the system voltage is good now so the alternator change was a success.

Take a look at the TPS and see if it is plugged in all the way and look to see if it cracked when you were working with it.

Back out the throttle stop screw some.
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Old 08-24-2022, 11:48 AM   #35
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Re: High idle on each start

You may want to look at this thread:
http://67-72chevytrucks.com/vboard/s...30#post9116230

He is running below1000 RPM while logging data with WinALDL, but he has not posted any closed loop data so far.

I posted this message:

After looking at data readings that seem so wrong I did some searches and reading on using WinALDL.

After reading on the http://www.winaldl.joby.se/ site I see the user has to make choices on how the data will display. Go to that site and click on the Click here for screenshots and descriptions of the different data displays link.
The user must make choices for how the TPS (Throttle Position Sensor), RPM (Revolutions Per Minute) and MAP (Manifold Absolute Pressure) sensor data will be displayed. Now I realize why the data logs the people a posting have readings that look so screwed up in these data sets.

The user can also chose to display the data in US values rather then metric..
The user can also pick which data will show.

I read much of the version history during development and saw on Nov 14 2001 changes were made on how the TPS data is displayed. This may have been when the choice selection was added in the display choices. I have noticed TPS irregularities in the logs people have been posting so they are most likely not setting things up correctly, or not realizing they have a choice to make.

My conclusion is that this software is great for an experienced person that has time to work with it and get to know the quirks of it, but for a newbie it is not going to be as easy as using a good scan tool.

If I was using this software I would establish my TPS voltage with a multimeter before using the software to know what to put in the choice boxes that control how the data is displayed. The RPM and MAP also has choice boxes which raises more questions.
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Old 08-25-2022, 09:10 PM   #36
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Re: High idle on each start

I have been through that info. Still, as you said, some of it's optional data to display is unknown to some of us newbies and we can be apprehensive about making changes. I'll play with that a bit next time I'm logging.
I am disappointed with the cable raising the idle speed and ignition advance. We don't get true idle data at 1000-1050 rpm. I see the other poster has the same issue though his rpms are 100-150 less than mine.
Here is what I did this week.
I went back to the basics and checked all spark plugs and timing.
I ran a can of Seafoam down it's throat, let it sit a while, then poured some more down it. I ran it hard out on the highway for a while.
I checked for vacuum leaks again.
Knowing you said I needed to get the iac down around 20 at idle I monitored the winaldl display while it was running paying attention to the IAC. At about 1000 rpm the iac was at 38 then all on it's own it began to start creeping up. I touched nothing. It reached 88. At that point I unplugged the iac and kept watching. 5 minutes or so later it began to drop, still unplugged mind you. It fell to 37-8 again and hung there, still unplugged, still idling around 1000. That iac is new also.
I turned the minimum idle speed screw back down. Some.
I ordered and put on a new Delco TPS.
I cleared memory by unhooking the batt cable. Again.
Now, the high idle on cold start is lower and it settles down to 600 est rpm within a couple minutes. Any restart now and it settles into a more normal rpm right away. That's good.
The negative is once again it feels like it wants to stumble and die in gear with foot on the brake at an intersection just like the minimum idle speed is too low. I tried driving with the laptop hooked up but that was a no go. With the increased rpm, of course it didn't want to die.
Watching the temp, it can get as high as 199 after a good drive but here in the driveway 187-8 is about all it will do even covering the grille with a heavy blanket. The Delco fan clutch for this truck is new and fully engages at about 188 so it has trouble reaching the 195 stat temp so I guess it is on the line of open loop and closed loop as far as data logging in my driveway goes? No one in town offers a Stant thermostat or even lists one. Maybe it would be beneficial to swap to an electric fan to allow it to run a bit warmer?
Now, after a couple days of drive time, I will do another data log maybe tomorrow and see what it looks like. Thanks for the tips.
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Old 08-25-2022, 09:59 PM   #37
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Re: High idle on each start

An IAC count of 20 at the correct idle with it warm and all accessories off shows the throttle stop screw is adjusted well.

With the engine idling faster then it should be, the IAC count will be high.

Once the IAC is unplugged with the truck running, the IAC position needs to be relearned. If everything is working correctly it will do a relearn on its own if driven at fairly steady speeds above 45 MPH.

The ECM does not know the actual position of the IAC. The ECM keeps track of the pulses sent to the IAC and assumes it moved with each pulse sent to it. With the IAC unplugged the ECM can not change the speed so it keeps trying and that is why the count continues to move.

There have been many bad thermostats, even new ones, for several years, that open to soon. These TBI trucks run rich if they run cold and often get heavy deposits on the valve stems so I am glad you ran some SeaFoam through it. You could heat a new thermostat in a pot on the stove and measure what temperature it opens at.

Years ago the NAPA house brand of thermostats were made by STANT. I have no idea if they still are.

I will watch for another log.
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Old 08-26-2022, 08:28 AM   #38
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Re: High idle on each start

I want you to try lifting the EGR diaphragm with your fingers on a cold engine and see if it has strong spring pressure and see if it feels like it closes well consistently.

I also want you to disconnect and plug the vacuum hose to the EGR valve and see if it has a more stable idle at lower RPMs when you drive it.
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Old 08-26-2022, 10:23 AM   #39
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Re: High idle on each start

Funny thing about the EGR. I had a CEL come on for the EGR. I purchased a cheap brand that had really good reviews. I cleared the code and the CEL did not come back on. A few weeks later I hit a washboard section on a county road near my house. The CEL came on for the EGR. I went home and cleared the code and went back through the washboard section and it turned on again. Now I know there is always coincidence possibility, but not twice in a row. I installed a Standard Motor EGR and went back to the washboard and it did not come on. When I changed the EGR I noticed that the spring was much weaker on the cheaper EGR, even though they were both new. Like CT said, a weak spring can cause problems. It may not close all the way or open on rough roads.
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Old 08-26-2022, 11:18 AM   #40
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Re: High idle on each start

That is interesting. Could be the 'cheap' egr valve was made with a weak spring.
I removed and cleaned mine months ago. It held vacuum and when I moved the diaphragm up it did affect the engine at that time. And there have been no codes. CEL does work. I also plugged off the vacuum line to the egr and drove it a couple of weeks like that with no difference felt.
I tell ya, when it stumbles at low idle it feels as if it was loading up on fuel but since I cannot log it at those low speeds, I can't tell if it's a low idle or over rich condition. It never smells rich though.
Can this iac operate "out of range" so to speak?
I know the ecm signals movements of the iac.
This low idle and stumble is what made me start freshening up under the hood in the first place. It's why I turned up the idle speed screw, which cured the low idle stumble and die problem but caused the high idle on every startup.
So, I'm back to square one.
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Old 08-26-2022, 12:12 PM   #41
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Re: High idle on each start

Quote:
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Can this iac operate "out of range" so to speak?
The minimum air rate (throttle stop screw) does not have to be in perfect adjustment.

You don't want the IAC count to every reach zero which means the IAC is all the way closed but the engine is still running faster then the ECM wants it to.

If the minimum air rate is to far off the other direction the engine will tend to flood or load up badly on a cold start.

What brand oxygen sensor did you use?

Does the stumble only happen after the engine warms up?
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Old 08-26-2022, 12:33 PM   #42
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Re: High idle on each start

I feel like a 25-50 rpm increase in base idle would be enough to stop the low idle stumble. Maybe worth easing it up a 1/2 turn or so on the stop screw to see.
Thing is with this cable running the rpm up when connected I cannot know what the iac counts are at normal idle speed. It has been displaying 38 counts at 1,000 rpm.
I'm not sure on the 02 brand. It's either AC or Bosch. I may still have the receipt. I don't buy the cheaper parts but that don't mean much these days.
Yes the stumble happens when fully warmed when I am stopped in traffic. It idles good for a few minutes then starts to slow down and feel like it will die. I tap the throttle and it picks back up but will do the same thing again. Sometimes I move it to neutral if I will be in a line for more than a few minutes.
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Old 08-26-2022, 02:31 PM   #43
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Re: High idle on each start

With a IAC count of 38 when at 1000 RPM you should be ok turning in the stop screw a little.

If you have a BOSCH oxygen sensor the first thing I would do is replace it. I would use a junk yard OEM oxygen sensor over a BOSCH after all the horror stories I have read.

You can hold the truck in open loop by unplugging the oxygen sensor and see how well it runs warmed up.
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Old 08-26-2022, 04:05 PM   #44
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Re: High idle on each start

Over the counter parts around here are very limited to the lowest priced parts due to customer choice. They don't stock much in the AC Delco brand. I just ordered an AC Delco tps from O'Reillys. The package said 'gm parts', not AC Delco. And it's made in china so I am skeptical of it's quality. I have been told that is the parts we'd get at a dealership also. I won't buy from them so I don't know.
I believe I'll turn up the stop screw 1/4 to 1/2 turn and see how it reacts. After that I'll unhook the 02 sensor for a bit.
The 02 is very active judging by the data log.
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Old 08-27-2022, 06:49 PM   #45
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Re: High idle on each start

I'm sneaking up on it with that idle stop screw and it is running some better. Here are a couple of screen shots from today. I did nothing else but turn up the idle stop today.
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Old 08-27-2022, 09:24 PM   #46
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Re: High idle on each start

It is in closed loop and in control.
Throttle position sensor is looking good now.
First capture has the coolant up at 190 which is good.
I don't notice anything that looks bad, but I wish the WinALDL did not need the 10K resistor to make it able to log data so we could get a log at normal idle speed.
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Old 08-27-2022, 11:14 PM   #47
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Re: High idle on each start

It does look like everything is working together better.
Cold startup idle speed is more like normal and drops down sooner. Restarts after warmup are at normal idle speeds. Idling in gear with AC on is smoother. I still may tweak the idle speed screw just a hair more and call it good.
I too am disappointed the aldl cable won't allow true idle speed data but it is what it is and that is more than I could see before purchasing it.
I intend to try to find a Stant thermostat and may even consider an electric fan to help engine warm up time and get it into closed loop sooner and stay there.
I love this truck and it is more pleasurable to drive again.
Thank you CT for all your help.
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Old 09-02-2022, 07:36 PM   #48
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Re: High idle on each start

Update:
It's been about a week now and it's running pretty good. As yet, I have not touched the minimum idle speed screw again.
My search for a Stant brand thermostat turned up nothing. I did read MotoRad purchased Stant brand some time back and is available at Advance Auto. I know nothing about MotoRad though.
I plan to go through my parts and put together an e fan and controller to try on my truck.
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Old 09-02-2022, 08:39 PM   #49
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Re: High idle on each start

I am keeping an eye on this thread.

It has been years since I bought a thermostat.
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For those of you that are wondering why you are not getting replies to your thread:
Did you give the model, year, engine, fuel system type, and transmission information?
If it is modified from what came stock from the factory, let us know that too.
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