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1G ISC...

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sonicselli

Proven Member
79
5
Aug 15, 2015
Lowell, Michigan
Sorry for yet another post on ISC's.

I'm having a serious idle surge problem. The idle will rev to (1500+) and drop below (1000) and repeat. I have changed a lot on the car since last year but before I post about whats changed I want to talk about my findings...

I pulled off the ISC to inspect it. Measuring resistance on the coils I got about 38ohms for each. Plugged into the car to see if the plunger even operates as it should and no it doesn't.... What many others experience claiming that it clicks and seems like it isn't receiving enough power... Same deal for me! I understand its a stepper motor so it is stepping once and not continuing its cycle to extract the plunger. Manually hooked up power to the ISC and I verified it does work. Okay so testing the connector making sure the ISC is even getting power I found on the center two pins are receiving voltage. The others are throwing me off... I'm testing for continuity on the pins to the chassis. I get some resistance on 2 of them. Then one will show some really low voltage(weird, thought only center 2 get voltage. or my multimeter is crazy) and the other has nothing......
I'm getting closer! I was kind of harsh on the ISC connector because it barely reaches to the ISC so there is potential for a broken connection. I looked at the back of the plug and it seemed alright.
I pulled the ecu and visually inspected the board and drivers. The ecu looks perfect. I know looks aren't everything so I was wondering if there is anyway to actually test the drivers or what my next step should be? I could measure the pin going from my dead connection on the connector to the ecu connector... hmm be right back!

Thank you for your help in advance!
 
A new one will project, retract and settle in. Just replaced mine and watched it before installing it.
 
The ISC is fed power via the two inner pins to the 4 coils. The ECU then grounds the coils in sequence using the driver chips to cause current to flow and the ISC to step.

The newer black ISC's typically measure about 38 ohms per coil. If the wiring between the ECU and ISC is tested good then it sounds like the ECU is damaged and one of both ISC driver chips need replacement.
 
Did OP figure out what was going on? Mine is still acting up. Replaced three ISC motors, sent ECU to ECMTuning, checked continuity to wires, checked power to both power wires at the ISC plug, and swapped the polarity of the coils because I’m running a 91+ ISC on a 1G.


I’m seriously at a loss.
 
Did OP figure out what was going on? Mine is still acting up. Replaced three ISC motors, sent ECU to ECMTuning, checked continuity to wires, checked power to both power wires at the ISC plug, and swapped the polarity of the coils because I’m running a 91+ ISC on a 1G.


I’m seriously at a loss.
Does the isc move or are you saying you still have an idle problem? If all you know is idle is bad then maybe the problem isnt the isc. Possible check egr. Fiav. Etc.
 
ISC does not move when I remove it from the car and supply power on and off. Just vibrates. That’s three separate ISCs as well. With the car running, ISC position starts at 120, slowly descends to 0, then slowly ascends back to 120. It repeats this until I shut the car off. Idle fluctuates about 100 RPM or so.


EGR and FIAV have been deleted.
 
Might be a stupid answer but maybe the PO swapped ecu connector pins to work a"90 ISC.
I checked the pins at the ECU, they’re wired for a 90 ISC. To compensate for this, I swapped pins at the ISC connector itself. Before asked, yes I’ve tried swapping pins at the ECU rather than the ISC as well.


I saw this on another thread as well. I only swapped the white and black pins. However, this image shows 4 pins swapped instead of two.
 

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I tried swapping all 4 wires (even though I figured it wouldn’t work because only two pins are different from 90-91+ models) and it didn’t work.

So, with one ISC installed, I unplugged it and installed one of my other ISC motors and sat it on top of my valve cover. With the car running, link showed it stepping to different positions, but the motor itself wasn’t moving at all. Just slightly vibrating.
 
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Let's get some answers here posters..... we would all like to find out what happened with the troubleshooting. I'm looking at you Anthony Boni and Sonicselli!
 
Let's get some answers here posters..... we would all like to find out what happened with the troubleshooting. I'm looking at you Anthony Boni and Sonicselli!
It’s been a while since I last thought about my ISC issue. I ended up buying a FIAV block off plate and haven’t been running a FIAV nor an ISC motor for the past year or so.

After sending the ECU to ecmlink and testing the harness for resistance, nothing out of the ordinary was found. I checked and reverified the pins on the ECU and in the motor connector. I then ops checked each ISC motor with a lantern battery, and none of them worked. I went through FOUR ISC motors, and still couldn’t get the little bastards to work. Two were used from reputable sellers, two were new. I bought the first one from somewhere online (can’t remember). Didn’t pass the operational check per the service manual, and it didn’t work in the car, so I sent it back for another. Same deal, wasn’t working. Said f**k it and deleted it. Reason I deleted instead of leaving plugged in is because if the bad ISC motor takes out the drivers in the ECU, it can take your ECU out with it.
 
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