ISC idle stepper servo diagnosing

[Guest]

I'm getting problems with my revs dropping when the air-con is on. The idle stepper visibly looks fine, all clean etc but it's a common cause in these situations.

Below is the method for testing these. Mine reads 45 ohms.

Is anyone else able to test theirs please and post up the results? You just need to unplug it and put the multimeter across some pins.

Also.. does anyone have a spare working one they'd consider parting with if this turns out to be the problem?

Cheers

 

[VOLK]

The replacement I bought to try fix my idle woes reads ~40Ω across all coils. My spare (original) reads similar resistance to yours I think, can test it again tonight.

From what I've read, they'll go open circuit if broken.

I'll send you my spare if you wanna test it.

 

[Guest]

Interesting.. cheers. Did the replacement fix the problem? If you could test your spare again that would be great.

 

[naughtika]

what should we get if the engine bay temp is around 40*c? or higher?

 

[Guest]

Not sure, but I think it increases the resistance. I tested mine off the car, so it wouldn't have been too hot. But I can't say for sure if it was the 20c they specify in the procedure.

In other news, I've been reading on Magna forums that it's not unheard of for the problem to be at the ECU end if the ISC tests OK. Capacitors leak and corrode the circuit board, yay.

Follow the links to the pics.

http://www.aussiemagna.com/forums/showthread.php?t=39821&p=579764&viewfull=1#post579764

 

[Guest]

Compatible part numbers for MD628056

E9T15296
MD614568
MD614978
MD628054

http://www.broomfish.co.nz/product_info.php?cPath=474_491&products_id=3737

 

[BCX]

In other news, I've been reading on Magna forums that it's not unheard of for the problem to be at the ECU end if the ISC tests OK. Capacitors leak and corrode the circuit board, yay.

From memory the only ECUs to suffer the leaking caps was around the 1992-1995 era. the ECU in those photos looks like a TR/TS ecu.

3000gt's of the same era suffered the same problem. Should be fixed by our ECU.

PS. I'll check out my ISC tonight if i get a chance.... mines the original unit (doesnt look shiney and new) and doesnt have any trouble with idling.

 

[Guest]

I hope so. Here's an interesting diagram for those who wonder how these work.

 

[VOLK]

My idle issue was TPS related.

If you've got resistance (within spec) on the coils and it idles up when cold, your ISC is working.

O/T: I had no idea about temperature effecting resistance, so I just read this: http://www.learnabout-electronics.org/resistors_01a.php

 

[BCX]

O/T: I had no idea about temperature effecting resistance, so I just read this: http://www.learnabout-electronics.org/resistors_01a.php

Indeed, the wonders of electronics... in a perfect world, nothing has a loss or resistance, and isnt affected by heat. even silicon in a transistor cant switch as fast depending on its temperature.

I'm sure Peter (poita) will be able to elaborate on this, think it's his job... electronics is just a hobby to me.

But yeah, if the 4 coils are in spec, and the unit is clean, might be worth checking elsewhere like tps, i've got mine set at approx 13% at closed - can check this via MUT. the ECU's ability to correct idle is also based on the idle switch - which is internal to the TPS.

Although sounds like one of your coils is out of spec if it's at 45ohms cold?

 

[VOLK]

TME_Steve found my TPS reading too high. Set to 13.3% and all was good once more. Still has the occasional higher than normal idle and slight hunt when using air-con though. Not to mention the 2000rpm cold starts being a little too high for my liking despite my BISS being wound almost completely in. Could be a vacuum leak somewhere, most likely BISS o-ring or the fact the BISS cap is missing/throttle body seals.

 

[Guest]

TPS is good, I have set it all up with Evoscan. But I'm going to check again tonight just in something has gone whack with the idle switch.

45 ohms seems OK for a warm ISC. I tested 2 other ones today and one was off a car just driven, it started around 45 and dropped as it cooled to 41. The other was well cool already, and read 41 ohms. It's about 30 degrees here today, so I'm taking that all as being within spec.

I confirmed that a CE Lancer ISC will work on our cars, just need to unscrew it and swap the pintle sides over. The rest of it is identical. I would guess the Magnas might be the same deal. This means lots more cheap sources for these. I'll upload some pics later.

Also, when the ISC is working correctly it will pull in a few mm when the ignition is on, then poke out a few mm when you switch the ignition off. I observed this with both a known good Legnum & Lancer ISC.

 

[VOLK]

Got mine from ebay, $120 delivered.

 

[VOLK]

Purchase decision made courtesy of Eddyvr4 taking a chance and finding they worked.

 

[VOLK]

Resistance between pins 1 & 2 = ~45 ohms, same for 4 & 5. 2 - 3 and 5 - 6 gave me odd readings, battery in my multi went flat. Will confirm tomorrow with a fresh battery.

 

[Guest]

So was the pintle exactly the same as ours, or the more tapered style?

I've been swapping them in and out of cars all day, one moment mine looks to be not working.. next moment it all looks fine.

I tested mine on another Legnum tonight, just doing the ignition on/off inspection. It hardly moved. But then got back home again, did the same test and it moves the few mm it's supposed to.

Reset the ECU (again) let it learn the idle. Same problem. It bumps high initially when the air con comes on, but then slowly drops down below normal idle. I watched Evoscan and I can see the ISC steps being put in to correlate this. It bumps up to about 50 steps, but then drops the steps right back and the idle falls below normal.

 

[VOLK]

Those readings were taken from my original isc, new one is still bolted to my TB. I'll rip it out and snap a pic for you.

Original:

eBay:

Judging by the ring of carbon on the new one it's been seating properly when stepped all the way out. Both old and new simply jiggle a little with ignition on, they don't step in or out.

 

[Guest]

Both old and new simply jiggle a little with ignition on, they don't step in or out.

Mine only does the little jiggle too, and I'm still having some problem with it when the A/C comes on. On the other Legnum I tested, it actually extended and retracted noticeably.

 

[VOLK]

I've seen vids of 3000GT and GTO ISC where they step out quite a bit upon being powered.

Still having a/c issues too, seems to hang at raised throttle for a few seconds after compressor clutch disengages. I've gotta a working logging cable now so I'll post some logs once I replicate and record the fault.

 

[AKKO]

Been reading over on ClubVR4 about diagnosing a similar issue.
Were these black or brown cased units, the former seems to be for N/A vehicles and not VR4s?