Need instructions to bench test the IAC, 94 LS400

[WeSki]

Hello All,

I'm looking for a tried and true test write up for bench testing the Idle Air Control IAC valve (AKA Idle Speed Control ISC) off a 1994 LS400 (165K miles) Part # 22270-50020. The 50020 IAC has the fixed coil mounted to it unlike the earlier LS400 that has the 3 screws holding the coil on the IAC; part # 22270-50010. 

I have attempted the bench test from Alldata but I'm not getting the desired results. My IAC measures 44 ohms for each of the 4 windings which according to Alldata is too high. The IAC doesn't function when I apply DC to the valve motor to move the valve open or closed. I could have a bad IAC but with reasonable and four even resistance readings I'm thinking I may be doing the valve test wrong.

Resistance test from Alldata: terminals B1-S1; B1-S3; B2-S2; B2-S4 all should be between 10 to 30 ohms. I've seen a posting that appears to be a lexus manual giving a range of 34-54 ohms. All four of my windings are right at 44 ohms.

Valve operation test from Alldata: Connect battery (+) positive to terminals B1 & B2, and the (-) negative to terminals S1-S2-S3-S4 in that order. The valve moves in the closing direction. Connect battery (+) positive to terminals B1 & B2, and the (-) negative to terminals S4-S3-S2-S1 in that order. The valve moves in the opening direction. 

I have one of each (50010 & 50020) IACs. When I do the valve operation test I can hear, feel, and see the valve bump (more of a wiggle) but that's it. I tried pulsing the the Negative in the sequence described but nothing. The 50010 gives me a little harder bump than the 50020 but neither move open or close. 

I'm assuming/guessing that I should be able to see the valve move open or closed when I apply DC to the valve motor in the correct sequence.

If anyone has performed this test successfully I would really like to hear from you and know if the valve should move with DC applied.

Thanks.

[Exhaustgases]

Fancy new website.....

 

I'm not sure but I think the IAC motor is a stepper motor, which means it needs a digital controller to work it. So unless you have a controller you aren't going to be running it on a bench. It couldn't be a normal motor because there would be no incremental control of it. It would either be all the way on or all the way off, it would be very tricky to stop it in any other position. And since things like the AC system and the power steering idle up valve etc. are in the system the valve does have to be modulated to suit conditions. And pretty much only a steeper motor will do it.

[WeSki]

Thanks Exhaustgases,

I haven't worked much with stepper motors but I am familiar with how they operate. I agree that a controller of sorts would be needed to move the valve open of closed but I have two test write-ups (Alldata & a Lexus manual) that both describe testing the IAC in the manner I described in my first post. In both test write-ups they show diagrams with the IAC connected to a battery; battery (+) positive to terminals B1 & B2, and the (-) negative to terminals S1-S2-S3-S4. There is one variation between Alldata and the Lexus manual; for connecting the negative to terminals S1-S2-S3-S4 Alldata uses the term of connecting the "negative to terminals S1-S2-S3-S4 in that order" while the Lexus manual reads "while repeatedly grounding S1-S2-S3-S4-S1". The diagram shows the positive and negative connected to the IAC all at the same time but that doesn't seem consistent with a stepper motor operation. I've tried every variation of connection the S1-S2-S3-S4 terminals to negative/grounding and nothing yet both test write-up lead me to believe that if done correctly the valve will move open or closed. Both test diagrams show using battery as the source to power the IAC but neither say what voltage the battery is, I can only assume that the battery is the 12 volt car battery but maybe 12 VDC is to much.

[WeSki]

After doing some internet research on stepper motors I made another attempt at testing my IACs. The procedure in my first post is correct. I tried a 9 VDC battery and also the 12 VDC car battery both worked fine. When applying DC to the IAC it is very difficult to see the valve move at least not by what my 20/20 vision can see. The momentary negative voltage must be applied in sequence and independently of each 'S' terminal i.e. apply negative DC to S1 then release, then apply negative DC to S2 then release, then apply negative DC to S3 then release, then apply negative DC to S4 then release. One round of applying and releasing negative DC to S1-S2-S3-S4 won't give you much movement in the valve in fact the first few times I attempted the the test I mistakenly ruled that either the IAC motor was bad but more likely that I was doing in wrong. My issue was that I wasn't repeating the apply and release cycle enough times to see significant movement of the valve. After repeating the negative DC apply and release cycle several times (S1-S2-S3-S4-S1-S2-S3-S4-S1-S2-S3-S4-S1...) I began to see significant close valve movement. Reverse the cycle (S4-S3-S2-S1-S4-S3-S2-S1-S4...) and after severe cycles you will see significant open valve movement.

Other learnings; the stepper motor on the IAC is a 125 position motor according to Alldata. The valve head does not spin or turn only moves open of closed. The shaft of the stepper motor is threaded (worm gear) that is threaded on to the valve head. As the shaft on the stepper motor shaft turns in the valve head the valve head move in and out on the stepper motor shaft opening or closing the IAC valve opening. 

This has been a real learning experience for me and hopefully not a waste of time and cyber but will be of value to someone someday.

[Exhaustgases]

Thank you for taking the time to figure it out, I may need it.  I would like to know how the controller in the car knows what position the valve is in, I don't think there are any limit switches are there?  Does it cycle from stop to stop?  And knows by what terminals where used to stop at say full open and see the current rise? I haven't played with stepper motors at all.

[WeSki]

I believe you are right, the controller would have to run the valve to full close or open and measure gases, fuel mixture or something because there is nothing on the IAC to tell the controller that the valve is in one position or the other. Once the controller determines the open or closed position I assume that controller keeps track of how many time it has sent signals to the IAC. I read a posting on the web were a guy reinstalled his IAC in the closed position and the engine would not start but took the car several starting attempts until it finally started. The poster speculated that the controller needed the attempts to recalibrate; I suspect he is right as from my research most engines won't start if the IAC is in the closed position.

[Exhaustgases]

The book says that after the engine stops the ecu continues to power the ISC valve to full open, so it must power it till it sees a voltage drop or an increase in current.

 

[Exhaustgases]

Notice how this site is still goofing up as noted by the goofy line through all my typing in the above post. I'm just glad it didn't switch to small font like it does sometimes.

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