You are correct that is its not a sensor. However it is monitored for faults, primarily by sending step changes and looking for changes in MAF air flow readings. And the ECU uses the map to tell the IACV where to move to achieve the goals of the ECU. Now we have an IACV that is in a different position from where the ECU thinks it should be, or when the ECU says go to step "X+Y" the results are not the same as when the old sensor was there. So the ECU continues to go by the old map of adaptive values. What terminal can we ground or drag high on the ECU to force it to relearn all the sensors and make a new map?

When I first bought my D1 this was a problem, and I tried every "trick" I could find on this site and others, to no avail. New IACV, used IACV, until I swapped the pair of the ECU and IACV. Of course, the ECU could have been bad,

 

You're assuming that putting the matching IAC into a different throttle body will produce the same results it did in the donor truck. That's not likely. And if the ECU monitors it through the Mass Airflow Sensor, it would know that it's in a different position than it expects and adjust, and what you're saying is that it doesn't know and doesn't adjust.

Can you tell me where you've gotten this information? I'd like to read it. Has anyone actually had a dealer reset these "adaptations" using Testbook?

No manufacturer I'm aware of provides an outside line that lets you reset any parameters. It's all done by the communications port. Manufacturers (and the government) don't want you screwing with this stuff.

The ECU has to have some type of "homing" routine to run the IAC up against one of the stops so that it knows the actual position. I'm going to see if I can see how this works this weekend.

I've also got a new IAC and a matched set of Theft unit & ECU on order to play with. I'm going to see if I can pull the proms and find out where the tricks lie. However, that's not likely to yield any results anytime soon.

I have done up schematics of the circuitry of the Theft unit and the Instrument Panel ECU, but any serious work on either of them will take some time as well. There's a 4 bit microcontroller in the instrument panel ECU made by OKI Semiconductor and it's obsolete. The micro in the Multifunction Unit is obsolete as well.

It's my intention, at some point, to know all I can about the entire truck before things start becoming unavailable. It may also be possible to do some improvements. Disabling the immobilizer signal between the ECU and Theft unit is high on my list. It wouldn't hurt to know enough to repair modules either. Fortunately the electronics in the Disco I is simple enough to decipher. I suspect that's not true of the Disco II.

 

I had my mine reset using test book 3 days ago. Or was it auto logic? Now I can't remember.

 

Was it to correct the problem with the adaptations?

 

One other thing to check along these lines is the cruise control paper-clip-type arm that attaches to the TB.

For some reason mine is like 1 or 2 mm too short, so it was constantly pulling the throttle open a smidge. I couldnt create enough slack by unscrewing the ball joint cap before it fell off, so I just had to disconnect it.

 

I'm thinking more along the lines that the ECU adapts to various sensor or mechanical wear things, like the throttle stop. In the case of the IACV, more gunk on it reduces the cross sectional area of the opening, so the ECU has to make it open wider to get the same result. When you clean the IACV, changing the performance of same, I don't know if ECU code instructions adapt in the reverse direction, or if they "assume" that that an IACV will be replaced by a dealer with a Testbook available to reset adaptive values or insert new ones. Not uncommon for programmers to write very tight routines on systems without a lot of memory or processing power. The ECU certainly does not know that you cleaned the IACV or the MAF, and if you have un-metered air (vac leaks) that can be a problem.

The monitoring of the actions of the IACV are documented in the GEMS ECU manual.

The adaptive value system is mentioned also:

The whole manual is attached. The variable names mentioned - I can't tell you if those are what is also used in the actual program.

I was hoping there was a sequence of events to make adaptive reset, without a Test Book or shop computer. Or a hidden reset button or pin to short on the ECU.

 

Thanks. Apparently the ECU does extensive checks on the IAC and WILL throw a code if it's out of range or failed in any way. However, it moves from 30 to 50 steps each attempt it makes (depending on direction), which should bring it into range inside of three to five starts of the engine.

On the other hand, the ECU measures the performance of the IAC using the mass airflow sensor. If the MAF is not performing well, low airflow measurements would be a problem.

Sounds like if you don't have a code the system has determined the IAC is OK. If the MAF is malfunctioning or dirty, the system could be letting in more air than it thinks, and not even try to adjust it. The only criteria for determining the MAF has failed is if the output voltage is out of range, and if it's just dirty, that won't happen.

 

So we can both be right. If the ECU had corrupt values, for any reason, and I changed my IACV (which may have looked dirty), the new IACV would not improve things. The ECU would keep using corrupt values. Changing the ECU got one that was not corrupt, and it quickly learned the new sensors and values. So if I swapped my old ECU back in, things might go back to whacko.

So perhaps one sign of corrupt values is the loss of precise idle control. And even though the stepper motor is working, the ECU is sending it to the wrong position. Because the ECU data is corrupt, the ECU believes this to be the correct action and makes no codes.

So is there a way to force the ECU to relearn all the values?

 

so maybe cleaning the MAF couldnt hurt as long as i do it with the appropriate cleaner?

 

According to the manual ,the ECU will continue to try to send it to the correct position based on MAF feedback. If it won't go, it throws a code. Your situation would contradict this by having it not throw a code.

I'm not saying you're wrong, but I still see no evidence of these "adaptations" for the IAC. And as someone who has designed similar systems, I just see no reason why there would be.

Of course I see no reason to have the VSS provide the ECU with information to limit the top speed of the truck either, and LR did that.

It's on my list to experiment with. My truck has bad vacuum hoses and is running an extremely high idle, so I should be able to duplicate the problems.

Part of the whole OBDII thing was federal laws to allow people to make engine repairs themselves or have it done by third parties without having to resort to the dealer or dealer tools. By having something on the engine controls that you need to access for a repair but isn't accessible defies the intent, if not the letter of the law.

And NO other cars that I've ever worked on save such information. You can ersae everything by just disconnecting the battery. In fact, now that I think of it, has anyone just tried disconnecting the battery for an hour or so and seeing if the problem goes away?