119 replies to this topic

[jack be nimble]

Not sure how to do this but i can always edit it later.

I had a blown ISC driver on my ECU, this is fairly common and is caused by blown/shorted coils in the ISC motor.
This results in bad idle control with no idle up for a/c and no idle up for power steer, no voltage compensation. also can make it harder to start when hot, but probably the worst is that at full throttle, the ISC is hanging down restricting air into the engine.

It can be diagnosed simply. If you start the engine hot or cold, it will start and rev around 1200-1300 rpm and quickly (5-10 secs) come down to the set idle, (900ish hot or 1000 cold). This is because the ISC starts at position 80 (out of 100 full open), but the warm idle is set by the BISS at around position 30. So the ISC rapidly shuts down to control the idle, so lowering the idle speed.

You could always unplug the ISC and note if there are any differences.
Or check the utube links in post #13

Checking the ISC for bad coils is done like this:


but, after fixing/replacing the ISC motor, you may still have no operational ISC.
this may be caused by blown ISC drivers inside the ECU. if you pull your ECU and have a look for this:
http://www.ecmtuning.com/wiki/driver01

This can be fixed by sourcing new/good used driver IC, and replacing the burnt ones.
There may also be burnt tracks as well under the driver that will need repair.

Here is my ECU after repair, I have installed a chip holder so that any successive blown drivers can be easily replaced (track damage aside. Fuses could also be installed if you wanted complete protection.

Edited by jack of all, 27 December 2011 - 02:35 PM.

[jack be nimble]

repair can be very time consuming. This is another I repaired recently that had blown tracks that are neatly repaired under the board.
prior to repair

leaky cap slime left from prior cap replacement

IC driver pulled like a bad tooth

IC holder installed, bottom of board soldering job

Top of board, socket installed

Had to fix the burnt tracks under the board with jumper wires, there was just too much damage to do anything else.
The red wire was a bit messy for my liking, so i redid it better and neater



so, after the repair, you need to buzz all connections, install and test for proper ISC operation

[Evo-00x]

Nice post. Time to test the ISC on the Nimbus 4G64 over the holidays!!

[jack be nimble]

here is a log of a cruise in my ute. i cant show it any better,the red line RPM, blue is ISC position, and green is throttle position
I have posted this to show how busy the ISC is when driving around. at idle it is at 30%, at full throttle it is at 100%, otherwise it sort of follows throttle position.


check out the diamonds on the phone cover. lol

Edited by jack of all, 20 December 2011 - 09:47 AM.

[jack be nimble]

If you arent game to solder on your own board, i can be persuaded to fix yours...

[leadfoot]

holy crap i should realy look into checking and getting mine fixed. i know i don't idle up with the ac or power steering and im almost certain it's not doing anything for cold starts either thanks for this write up i'll check all that now.

[dafurn]

I like the idea of the socket for the driver chips nice work. I replaced some before I knew what they controlled and then had to do it again after the faulty isc blew it again. That would be heaps easier. Do have a source for new driver chips?

[jack be nimble]

I have 50ish new ones, if you want to pm me

[leadfoot]

i think i have a spare i'll test it and get back to you although i have a feeling i might have dead isc controlers

[Evo-00x]

If you arent game to solder on your own board, i can be persuaded to fix yours...

Thanks man, I appreciate the offer. I'll check the Nimbus after Xmas and test the resistance on the ISC pins. If the ISC is OK, then I'll open the ECU to see if its damaged.
I never ever have any issues with the ISC on cold starts, it starts first go everytime and idles fine.
But after doing a short run in the car and turning off the engine, say to refuel at a servo, or drop in somewhere for a few minutes, about 1 out of 3 times the engine will start up and keep the revs high between 2,000-2,500rpm. Then the idle will go up and down like as if the engine its hunting.
To get rid of this problem, I would have to turn the engine on and off. Sometimes it stops stepping up and down after a couple of shutdowns, but other times it wont stop at all and I just end up driving to where I have to go.
Then when the engine starts from cold again, the problem isnt there.
As I only drive the car to work and back most the time, its cold start on the way to work and a cold start on the way home... rarely doing warm starts unless its for refuelling. Thats why I've been able to live with it for a while as I couldnt be assed fixing it since owning it for the last couple of years

[dafurn]

I have 50ish new ones, if you want to pm me

Thanks mate. I ll have a look at work first though should have them.

[jack be nimble]

I have done a bit of research on a couple of ecu and can give you all some info for checking the ecu for burnt drivers and tracks.

Looking at the ic drivers so you can read the writing, (inside ecu) the pins are numbered 1-8 from left to right. There should be no combinations of pins that are shorted.
With diode check selected on your multimeter (looks like this ->|- ) place leads As follows:
Black lead- pin8, red lead- pin7 - reads ~0.7
Black lead- pin8, red lead- pin1 - reads ~0.7
black lead- pin5, red lead- pin4 - reads ~0.5
red lead- pin4, black lead- pins1,7,2 - reads ~0.5
red lead- pin4, black lead- pins 3,6 - reads ~0.7

You can test the ic drivers while they are fitted to the ecu, and the reading is fine anywhere between 0.45 to say 0.8. This measures all the transistors and diodes inside the chip, if you reverse the leads there should be no connections (open curcuit). There should be no shorts between any combinations of pins.

To test the tracks of the ecu, we need to measure with a ohmmeter. I used the 200 ohm scale to measure between icdriver pins and the ecu pins for the loom.
Ic105 pin1- ecu pin18- reads 0.9
Ic105 pin7- ecu pin 5- reads 0.9
Ic106 pin1- ecu pin17- reads 0.9
Ic106 pin7- ecu pin 4- reads 0.9

To be confirmed:
Checking loom wiring continuity:
Isc pin1- ecu loom pin4
Isc pin4- ecu loom pin5
Isc pin3- ecu loom pin17
Isc pin6- ecu loom pin18
Pins 2 and 4 I haven't traced yet, I think they are power and switched power, these are the wires to fuse if trying to protect the ecu from burnt tracks.

Edited by jack of all, 16 April 2012 - 02:06 AM.

[jack be nimble]

you tube link for a good working ISC:


and the bad one:


as you can see by the temp gauge, it is cold and thats why the idle settles at the 1100 rpm mark, as it warms up, the revs drop to around 900

Edited by jack of all, 27 December 2011 - 02:32 PM.

[leadfoot]

thanks to this i manages to diagnose and fix my isc problemb. my car now idles correctly (does not drop stays constant) when the ac kicks in allowing me to drop my idle by 400 rpm.

it's amazing the amount of gunk and crap that accumulates in this area so have a couple of can of carby/ electric contact cleaner handy and an o ring to replace the one in there.

[EVL20T]

Im gettin 42.3 Ohm between each coil

[nigel_a]

So my car was acting up, tested the isc and it was dead. Replaced it and the car ran great for a week, now it's acting up again. Checked the isc and it's ok, checked the ecu and it looks ok. What else could it be?

[Gianni]

Acting up how? Could be sensors, could be vac leak. Could be lots of things

[nigel_a]

Doesn't idle up with the ac on or with power steering, no cold start, struggles to regain idle when you give it a rev. Pretty much behaved like an isc that's disconnected or not working.

[JETGSR]

i might need to call you passion fingers too!

it was working fine! and BTW there is no warrany on that part!

check the plug for the IAC

[jack be nimble]

You can check the drivers and wiring from the isc plug, and this is the bit I need to add to complete this sticky, but unfortunately I don't have my note book here to add this information.


Take out your isc and plug it into the harness, get someone else to watch it. When you click ignition key to the run position, the isc should move (retract maybe?)

Try this and report back.
If it doesn't move there is an issue with either the isc, wiring, drivers, or ecu circuit board.
Don't panic, even burnt boards are repairable.

Edited by jack of all, 08 April 2012 - 12:25 PM.