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TR 300000
02-09-2006, 09:53 PM
I got a multimeter and did the recommended checks on the TPS and ISC today looking for solutions to my rough idle problem. The TPS checked out OK according to what the manual says.

The ISC was harder though.

I put the multimeter onto the proper pins checking for resistance. The manual says that "if the meter indicates high resistance, renew the ISC motor." Unfortunately it does not provide a figure to compare to.

My tests got a resitance of .05 on all pins. I'm new to this. Is that low or high? I believe I had the meter set right on the 20k setting in the bottom section of the selector.

Killbilly
03-09-2006, 06:24 PM
http://www.nardek.com.au/testisc510-10.htm

That's what you should be doing :D

TR 300000
04-09-2006, 04:48 AM
Thanks but I'm still unsure:

"REPLACE ISC MOTOR IF ANY RESISTANCE IS NOT 28-33 OHMS AT 20 DEGREES"

20 degrees? 20 degrees what?

stereo_god
04-09-2006, 05:48 AM
20 degrees C as in ambiant temperature of the air as you measure it. resistance changes with temp

TR 300000
04-09-2006, 08:46 AM
Thanks, this is cool. I'm sure mine is stuffed now, so I'm going to get a replacement. Then I will fit it and set the idle (cos I stuffed around with the throttle stop) and all will be sweet once again.

RuSSiaN
04-09-2006, 12:56 PM
clean the TPS

TR 300000
04-09-2006, 01:18 PM
Yeah cleaned the TPS thoroughly the other day with atoothbrush and contact cleaner. Gave me a little more smoothness but ISC still not working.

Bought a new ISC today and fitted it. No improvement. Am working through advice from the forum before I yell too loud for help.

RuSSiaN
04-09-2006, 01:46 PM
Yeah cleaned the TPS thoroughly the other day with atoothbrush and contact cleaner. Gave me a little more smoothness but ISC still not working.

Bought a new ISC today and fitted it. No improvement. Am working through advice from the forum before I yell too loud for help.


How are the igntition system ie: spark plugs, leads, dist cap and rotor

(when changing spark plugs make sure they are the correct gap)

air filter condition?

TR 300000
04-09-2006, 02:50 PM
Yep, all those plugs etc. should be fine.

I've just reset the throttle stop adjustment back to factory spec and adjusted the SAS (on top of the thottle body) up 2.5 turns to get the engine idling at 850 rpm. Screw is very loose and turns easilly. If I put the car in gear or turn on the ac and the idle plunges down to 500-700 again and the car vibrates like crazy. The nes ISC does nothing to pull it back.

I need to get the multimeter and check the current coming into the ISC. The manual says:
"Turn the ignition on and check for power on the red wires of the harness connector corresponding to the ISC motor terminals 2 and 5"

How do I do that? One probe in the socket and one on earth? If earth is that the car's body? Or should I be putting one probe in each socket (2 and 5)???

stereo_god
04-09-2006, 04:20 PM
use the volt meter because if there is no voltage no current will flow. put the black negative wire on the multimeter on the car chasis as you would to an amp or head unit. then put the positive in the correct pins on the connector to check if voltage is comming through

TR 300000
04-09-2006, 06:08 PM
Thanks stereo_god.

I checked it out and there's over twelve volts coming through each of the power lines.

So,

I've got power, a tested and working TPS, and a tested and working ISC. Iv'e got a throttle stop reset to factory specs. I've set the unladen idle at 850-900 rpm using the SAS.

Still the bugger won't idle up when the ac is switched on, or when I put her in gear, or when the electric fans come on, or when the power steering goes into action.

Where to from here.....

gst74
04-09-2006, 07:14 PM
Thanks stereo_god.

I checked it out and there's over twelve volts coming through each of the power lines.

So,

I've got power, a tested and working TPS, and a tested and working ISC. Iv'e got a throttle stop reset to factory specs. I've set the unladen idle at 850-900 rpm using the SAS.

Still the bugger won't idle up when the ac is switched on, or when I put her in gear, or when the electric fans come on, or when the power steering goes into action.

Where to from here.....


i had exactly the same problem with my ISC. It wouldn't idle up and it checked fine with the multimeter. I ended up making a LED array and plug it into the ISC plug. It consisted of 4 LED's. when i turned the A/C on 3 LEDs would light up but never the fourth. I traced the wiring back to the ECU and found them to be all perfectly fine. I then removed the ECU and started tracing the circuit board. I found a break in one of the tracks. It was caused by a leaky capacitor. I have attached a couple of pics of my ECU.

The first pic shows the entire board and the red square shows where i removed the capacitor.

http://i115.photobucket.com/albums/n305/gst74/100_0572withtext.jpg

The second pic shows a close up of the area.

http://i115.photobucket.com/albums/n305/gst74/100_0573withtext.jpg

You can zoom in pretty close with these pics as there a fairly hi res.

You can see where it has corroded the tracks. I repaired the board by soldering a jumper wire to the back of the board on either side of the break. The track actually goes through the board from one side to the other underneath this capacitor. The capacitor looked completely normal and fine while it was in place but once i removed it i could see where it had leaked. Mitsubishi wanted to change the ISC motor and charge me $300 for it. It cost me about 20 cents to repair the board and replace the capacitor.

This may or may not be your problem, i just thought i would share my experience.

i would not recommend this job to anyone who has not got some electronics experience and has never soldered on a board like this. ECU's are expensive to replace!!!

TR 300000
04-09-2006, 09:01 PM
Wow! I can't thank you enough for your reply. I was beginning to wonder about the ECU. Now it looks seriously worth looking into.

Thanks so much for taking the time to post your photos. They'll be a great help to me when I pull mine out to have a look. You never know, mine might be just the same. If so I'll take it to be repaired by someone who knows how to weild a soldering iron. Probably can get it tested somewhere too.

Thanks heaps.


i had exactly the same problem with my ISC. It wouldn't idle up and it checked fine with the multimeter. I ended up making a LED array and plug it into the ISC plug. It consisted of 4 LED's. when i turned the A/C on 3 LEDs would light up but never the fourth. I traced the wiring back to the ECU and found them to be all perfectly fine. I then removed the ECU and started tracing the circuit board. I found a break in one of the tracks. It was caused by a leaky capacitor. I have attached a couple of pics of my ECU.

The first pic shows the entire board and the red square shows where i removed the capacitor.

http://i115.photobucket.com/albums/n305/gst74/100_0572withtext.jpg

The second pic shows a close up of the area.

http://i115.photobucket.com/albums/n305/gst74/100_0573withtext.jpg

You can zoom in pretty close with these pics as there a fairly hi res.

You can see where it has corroded the tracks. I repaired the board by soldering a jumper wire to the back of the board on either side of the break. The track actually goes through the board from one side to the other underneath this capacitor. The capacitor looked completely normal and fine while it was in place but once i removed it i could see where it had leaked. Mitsubishi wanted to change the ISC motor and charge me $300 for it. It cost me about 20 cents to repair the board and replace the capacitor.

This may or may not be your problem, i just thought i would share my experience.

i would not recommend this job to anyone who has not got some electronics experience and has never soldered on a board like this. ECU's are expensive to replace!!!

Killbilly
05-09-2006, 04:42 AM
That cap leak is a common problem too...worth checking out.

stereo_god
05-09-2006, 04:53 AM
just for clarification how did you make the led thing gst74. its just a resistor and led. but which way do you put them in the connector to test it

gst74
05-09-2006, 05:17 AM
just for clarification how did you make the led thing gst74. its just a resistor and led. but which way do you put them in the connector to test it

It was simply an LED and resistor connected in series. I made four and then connected them as shown in the attched pic. When you turn the the key to ignition(but dont start it) the ISC should go fully open and when you turn the ignition off it should go fully closed. With this connected you should see all four LED's pulse one after the other. It is very quick though so you may have to turn it on and off a few times.

If you remove the ISC motor and leave it connected to the wiring harness and turn the ignition on you can see it move. If it just pulses in the one spot without retracting and you have tested the resistance of all the coils of the ISC then there is a good chance that it may be the wiring between the ECU and ISC or it could be a problem similar to mine

stereo_god
05-09-2006, 05:51 AM
what value resistor did you use i calculate it to be bout 200 ohms, what did you use?

gst74
05-09-2006, 06:12 AM
what value resistor did you use i calculate it to be bout 200 ohms, what did you use?


sounds about right depending on the LED you use. When using a Light Emitting Diode (LED) as an indicator, use the following formula to determine series resistance for various voltages: R = (E - 1.7) x 1000/I, where R is the resistance in ohms, E is the supply voltage (DC) and I is the LED current in milliamps.

Eg. to operate the LED at 20mA, for 6V, use 220 ohms

9V use 390 ohms.
12V use 560 ohms
24V use 1.2k ohms

The pulses are very short so if the resistor is to big, the LED doesn't light very brightly and makes it difficult to see. So although for 12v is says to use 560 ohms i would use something smaller.

stereo_god
05-09-2006, 05:39 PM
actually leds need 2 volts 20 mA normally so you want to drop 4 volts. R=V/I

R=4/0.02
R=200 ohms

gst74
05-09-2006, 07:06 PM
actually leds need 2 volts 20 mA normally so you want to drop 4 volts. R=V/I

R=4/0.02
R=200 ohms


Where did you get 4 volts from. In the picture i drew there are four sperate LED's and resistors, each pair connected to the centre 12v pin and to the outside ground pin. The ISC is controlled by alternately grounding the four outside pins. Therefore you have to treat each as there own circuit.

I agree with you saying that LEDs have a forward bias voltage of 2v (i was looking at on old uni chart). So the correct values for the resistors would be.

voltage drop across resistor is equal to supply voltage - forward bias of LED

that eqautes to 12v-2v = 10v

Max forward bias current of an LED varies but is typically 20mA

R=V/I

R=10/0.02

R=500ohms.

But as i said it doesn't really matter. The LED is driven so quickly and for such a short period of time that it will do no damage to the LED or the ECU.

stereo_god
06-09-2006, 05:44 AM
my bad somewhere earlier it said about 6 volts and thats what i worked it out on. that will teach me to be lazy and not go outside and measure it myself

typhoon
08-09-2006, 03:17 PM
My limited experience with ISC motors on the Astron and V6 engines with high mileage suggests the best test is to see if they bounce off the side of the garbage bin as they go in.
Meaning, if you are having issues with your idle when any of the accesories load the engine up (power steer, auto in gear, A/C) it is always ISC related. If the idle is fine when warming up, and in neutral it is an ISC problem. Throttle position sensor, unless waaaaay out, shouldn't affect idle. TPS will create a stumble off idle as throttle is opened though.
The only thing that controls an increase in idle speed as accesories load the engine is the ISC. It doesn't control hot idle, the bypass air passage(screw adjuster on throttle body) does this. And cold idle/warm up is controlled by the cold start device (forget the name).
Considering they are turning up on Ebay for under $100, I just replace them if I suspect them. Haven't been wrong so far! Same with O2 sensors as well, any car I buy with over 150k kms on it, I just replace it if it looks old. It works out cheaper with reduced fuel consumption, over the time I own the car.
Oh yeah, don't drop the new ISC as you install it!:shock:

Regards, Andrew.

TR 300000
09-09-2006, 08:32 AM
I feel a bit glum because I have two fully functional ISC but neither are working as they should. As was noted above, it looks like my ECU may have a fault. I don't know how much these are to replace yet (secondhand I suppose). The clean up I did on the TPS has smoothed the car out a lot though.

I guess I'll just have to live with the situation for now.

STEALTH TR
09-09-2006, 05:40 PM
g'day mate, i also have TR and i hated the way it would shake in idle in drive at the lights, anyway today i replaced the rear engine mount just as a stab in the dark approach and it came up trumps

it cost $60 from bursons and their wasnt too much in fitting it myself but it was well worth it, its like a different car. if you havnt already tried engine mounts give it a go, could be a cheap fix mate

RuSSiaN
09-09-2006, 06:02 PM
with most magnas, theres alot of things that can affect idle

I suggest searching, we have all tryed to fix the problem


yours may be and engine mount, someone else a pcv valve, someone else crack in distributor cap etc

mine was the TPS was not clicking side to side properly (had a build up off crap blocking it)

I suggest searching, thats for all gens of magnas

my cousins Xi Verada even has a idle problem

typhoon
10-09-2006, 06:04 PM
How do you know your ISC's are fully functional? Testing them is a waste of time. Replace them. I replaced one that tested O.K, and it changed everything. Just because the electrical part tests O.K, does not mean the pintle moves correctly.They are a sub $100 part, and if it is not gone at over 200k kms, it is about to go anyway.
If the computer has problems it will throw a code, try retreiving the codes (if any) as per the manual.

Regards, Andrew.

TR 300000
10-09-2006, 07:16 PM
I believe it is fully functional because it is brand new purchased last Tuesday ($100). It and the old one both test fine with the multimeter. The old one is itself five years old being a replacement for one that died at about 130,000 km (that one cost me 350 dollars).

I shall try retreiving the codes, but I understand this can be difficult with a digital multimeter. I shall re-read the manual and see.

TR Stealth: $60 for an engine mount is a lot cheaper than I though they were. I could well try this in the near future.


How do you know your ISC's are fully functional? Testing them is a waste of time. Replace them. I replaced one that tested O.K, and it changed everything. Just because the electrical part tests O.K, does not mean the pintle moves correctly.They are a sub $100 part, and if it is not gone at over 200k kms, it is about to go anyway.
If the computer has problems it will throw a code, try retreiving the codes (if any) as per the manual.

Regards, Andrew.

gst74
10-09-2006, 07:34 PM
How do you know your ISC's are fully functional? Testing them is a waste of time. Replace them. I replaced one that tested O.K, and it changed everything. Just because the electrical part tests O.K, does not mean the pintle moves correctly.They are a sub $100 part, and if it is not gone at over 200k kms, it is about to go anyway.
If the computer has problems it will throw a code, try retreiving the codes (if any) as per the manual.

Regards, Andrew.


You can tell if an ISC is fully functional by removing it from the throttle body leaving the wiring loom connected. When the ignition is turned on the pintle fully retracts. When the ignition is turned off the pintle fully extends. If it doesn't do that then it is faulty or the wiring to it or the ecu is faulty. Just because they are a relatively cheap part you don't just change them because you think it may be the problem. Thats what service centres do because they dont want to spend any time trouble shooting.

The ECU will not throw any codes for the ISC. If the ISC stops working then the ECU does not know that it has stopped. Apart from the injectors the ECU only returns fault codes for sensors.