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The dreaded idler stepper.


ross mcdermott
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Hi Team, can any of you bright sparks out there tell me how to set the voltages up for the idler stepper motor. I am so tired of forking out $00s to the workshop while they try and do snow job on me. It took them just a few minutes a year ago and they stung me over 200 big ones. I have the gear but not sure which pins should be set up to which voltage. All answers gratefully received.

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Hi Team, can any of you bright sparks out there tell me how to set the voltages up for the idler stepper motor. I am so tired of forking out $00s to the workshop while they try and do snow job on me. It took them just a few minutes a year ago and they stung me over 200 big ones. I have the gear but not sure which pins should be set up to which voltage. All answers gratefully received.

Not sure what you mean... there's no adjustment on the idle stepper motr. Do you mean the Throttle Position Sensor ?

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I'm guessing this is a V8 in which case this might be better asked in the International section where the V8 gurus lurk

Thanks James, I will have a quick sticky beak there and see what they come up with. Sorry I should have said it is a 3.9L. Love the vehicle but dont even have any of the diagnostics codes. Wonder if a set of Rune Stones would work or maybe a Horoscope for a landy......... :P

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Not sure what you mean... there's no adjustment on the idle stepper motr. Do you mean the Throttle Position Sensor ?

Dave, my face is red. I probably sound as thick as two short planks, Forty eight hours ago I did not even know what the darn thing was even called. When it crapped out last time he got his digital VM and set up the voltages to the stepper. That is what I meant by the adjustment. I should have paid closer attention to the point he put his meter on. They were deliberately playing smoke and mirrors with me. I can actually do all this stuff, it really is a pretty simple setup masquerading as high tech which it aint, it is just that I am not familiar with the vehicle and don't have the local knowledge. A proper service manual would probably be a great place to start I guess. The workshop said they are sealed for life, throw it away and get a new one $500). Well I can tell you..duh!.....I carefully dismantled it, no easy feat. Got my wife's embroidery magnifying lamp and carefully cleaned the whole thing. Apparently they get all gummy from the aromatics in the fuel vapour floating about in the Plenum. Anyway, I can tell you the wiring is as fine as a hair but have worked on tons of microprocessors so none of that was a problem, reassembled the whole thing and .........and........duh! I doh wanna. Naughty words, wrath on all things holy, stuff it, large Scotch and plan B. LR4x4 Guru time. Do they use a polarity change for up and down or just a simple voltage shift? What do I do now?

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Or the MAF even? :rolleyes:

The MAF.........of course.....I should have thought of it. What the heck is a MAF. Here it is the Ministry of Agriculture and Fisheries. Weve gotta lotta both. (Outnumbered 60:1 by sheep and some of those sheep are pretty smart but ugly.) Seriously what is the MAF?

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The MAF.........of course.....I should have thought of it. What the heck is a MAF. Here it is the Ministry of Agriculture and Fisheries. Weve gotta lotta both. (Outnumbered 60:1 by sheep and some of those sheep are pretty smart but ugly.) Seriously what is the MAF?

Mass Air Flow sensor, the air flow meter. Squareish box just downstream of the air filter in the air intake plumbing with electricity going into it.

As to "what system" the question means what EFI system is fitted to the engine - there are a few different sorts. If you don't know then post up the age of the vehicle and a picture of the engine bay and we can figure it out :)

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OK Ross, calm down, step away from the soldering iron, go to the technical archive index and find yourself the V8 Hotwire EFI diagnostics guide.

You seem to be crossing several components here:

- The idle stepper valve. As has been said, they do stick but that is a dirt issue not an adjustment one. It's the thing on the back of the plenum with 4 wires going in.

- The throttle position sensor, which is on the side of the intake mouth of the plenum. It has 3 wires going in (red, green, yellow usually) and does require setting to a specific voltage at rest.

- The airflow meter (MAF) which is the big useless lump between the plenum & air filter. You can adjust a bypass screw on them, and if you really want to you can open them up and prat about but I really wouldn't.

Since this is now my 2nd post I think it's well overdue that I suggest MegaSquirt instead of all this bother :lol:

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Anyway, I can tell you the wiring is as fine as a hair but have worked on tons of microprocessors so none of that was a problem, reassembled the whole thing and .........and........duh! I doh wanna. Naughty words, wrath on all things holy, stuff it, large Scotch and plan B. LR4x4 Guru time. Do they use a polarity change for up and down or just a simple voltage shift? What do I do now?

Sounds like whoever set it up was being a bit "creative" with the truth.

The idle control is a stepper motor and, as you've already found out can get gunged up and from time to time need cleaning. As long as you're careful they can be taken apart (or at least the plunger part) and cleaned.

The unit is basically self calibrating. When you turn the ignition the ECU moves it either all the way in or all the way out (can't remember which on the standard setup, on mine it moves it out. It deliberately winds it out further than it should be able to and the design of the unit allows it to effectively calibrate it's position by doing that. It then moves a predetermined number of steps to the cranking position. Once the engine starts it then closes the stepper down in 3 stages to reach normal idle speed.

If you plug the unit in while it's not screwed into the plenum chamber and turn the ignition on you should see it move to an extreme BUT if it is allowed to wind out too far the spring will propel the plunger to the darkest recesses of your engine bay/drive/garage. It's not impossible but it is quite complicated to move the motor "manually" one step at a time. The 4 wires are arranged in pairs, each pair controlling a different winding. Moving the motor is "just" a case of providing 12v across the appropriate winding, reversing polarity as needed... it's a LOT easier to get the ECU to do it :) It's a bipolar stepper motor - lots of info on t'internet on how they work and how to drive them. As the motor rotates the screw thread on the plunger winds in or out depending on the direction the motor is rotating.

If you're happy it's working correctly just stick it back in and turn the ignition on/start the engine a couple of times and it should sort itself out. If you want to test the winding continuity you should get a reading in the region of 50 ohms (off the top of my head) across each pair with no connection between the pairs.

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One more thing, as it sounds like you don't mind playing with this kind of stuff, I have a circuit I use to allow my Megasquirt ECU to control the Idle stepper and it also has a manual mode where I can wind the stepper in or out by pressing the appropriate switch on the PCB. It uses a simple PIC chip to control a stepper driver IC. I've used it regularly to test steppers from other vehicles.

The Megasquirt 1 ECU can't control a stepper motor directly so this board in it's normal mode translates the PWM output from Megasquirt into a pintle position.

More on the board (schematics, pcb layout etc....) here... http://www.msextra.com/viewtopic.php?f=67&...71&start=40

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OK Ross, calm down, step away from the soldering iron, go to the technical archive index and find yourself the V8 Hotwire EFI diagnostics guide.

You seem to be crossing several components here:

- The idle stepper valve. As has been said, they do stick but that is a dirt issue not an adjustment one. It's the thing on the back of the plenum with 4 wires going in.

- The throttle position sensor, which is on the side of the intake mouth of the plenum. It has 3 wires going in (red, green, yellow usually) and does require setting to a specific voltage at rest.

- The airflow meter (MAF) which is the big useless lump between the plenum & air filter. You can adjust a bypass screw on them, and if you really want to you can open them up and prat about but I really wouldn't.

Since this is now my 2nd post I think it's well overdue that I suggest MegaSquirt instead of all this bother :lol:

Megasquirt...........have you already met my brother? :P I guess that is like CRC or something similar. You are right though, I got the stepper bit right but did not know about the "throttle posn sensor. Will go and have a sticky beak later. I guess this is what the witch doctor was playing with. Will also go to the site you referred to. Will let you know what happens and thank you for the advice. Gorgeous summer here this year. Copious days of 30C + and Feb is our hottest month. Son #2 is in London (snigger snigger) we enjoy talking to him about "hot days in Canterbury NZ, salmon fishing, 6lb rainbow trout, eating alfresco, balmy evenings under the stars. Got to get him home somehow. If this does not work nothing will. Thanks mate, really appreciate the info.

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OK Ross, calm down, step away from the soldering iron, go to the technical archive index and find yourself the V8 Hotwire EFI diagnostics guide.

You seem to be crossing several components here:

- The idle stepper valve. As has been said, they do stick but that is a dirt issue not an adjustment one. It's the thing on the back of the plenum with 4 wires going in.

- The throttle position sensor, which is on the side of the intake mouth of the plenum. It has 3 wires going in (red, green, yellow usually) and does require setting to a specific voltage at rest.

- The airflow meter (MAF) which is the big useless lump between the plenum & air filter. You can adjust a bypass screw on them, and if you really want to you can open them up and prat about but I really wouldn't.

Since this is now my 2nd post I think it's well overdue that I suggest MegaSquirt instead of all this bother :lol:

You beauty. Just had a quick look. 3 wires, yellow green and brown. Little black widget on the intake side of the plenum and directly opposite the throttle control. Where do I set the votages up?

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One more thing, as it sounds like you don't mind playing with this kind of stuff, I have a circuit I use to allow my Megasquirt ECU to control the Idle stepper and it also has a manual mode where I can wind the stepper in or out by pressing the appropriate switch on the PCB. It uses a simple PIC chip to control a stepper driver IC. I've used it regularly to test steppers from other vehicles.

The Megasquirt 1 ECU can't control a stepper motor directly so this board in it's normal mode translates the PWM output from Megasquirt into a pintle position.

More on the board (schematics, pcb layout etc....) here... http://www.msextra.com/viewtopic.php?f=67&...71&start=40

Dave you are a genius, at last some info I understand. You are talking my language. (Lectured in digital electronics till I got an honest job lol. Thanks a lot for the info. Murphys law......it is all running like a new one now. Had a best guess at the wiring, they all fell of of course. Brother is that fine wiring or is that fine wiring. Anyway, mummy will be fwilled wid me. :lol: Thanks again. Is this a good time to join the cast of thousands and ask why the heck does my cruise control keep dropping out or should I wait until peace reigns eternal internationally!

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Mass Air Flow sensor, the air flow meter. Squareish box just downstream of the air filter in the air intake plumbing with electricity going into it.

As to "what system" the question means what EFI system is fitted to the engine - there are a few different sorts. If you don't know then post up the age of the vehicle and a picture of the engine bay and we can figure it out :)

Kind offer, thank you. I will take a piccy but have a clean up first. The engine not me,................oh ok both then. Found the MAF just where you said it would be. Is there some tech data somewhere I can read about it? Does it need a clean up inside every so often to ensure clean and efficient operation? The filter would get most I guess but then again.........! Did not know there was a selection of EFI set ups. It would be good to know what Vs I have. Have to say that the vehicle has given pretty good service really and it has been to places that God never intended anything with wheels on should ever go. The perils of a dry fly fisherman you see. That and those big piles of dirt called the Southern Alps. Had the President of the Tokyo Bank and his gorgeous PA in the vehicle with me one day. I did not know that the Japanese could turn white. Have never seen knuckles so tense and white or teeth so firmly clenched. Must have cost him a fortune in orthodontic treatment when he got back to Japan. He never uttered a sounfd from the moment I left the road and started climbing up the side of a few "little hills". His PA sat in the back and just made squeaky noises. I thought it was just all in a days good fishing. We got the trout though. Fantastic silver bellies and rainbow tops. Gorgeous day. Hated every bloody minute of it. :P

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