need ISC help

L train · Sep 6, 2011

ok so i have some bad idle surge i suspect its the isc or rather the wiring to the isc ( i have replaced everything so its got to be a wiring issue i have 0 boost/vac leeks) sometimes when i drive for 30 min or so it will idle just fine, but not always more often i pull up next to a car most likely a riced civic at a stop light and my car starts bucking from idle surge....not pimp

i looked in my book for how to test this issue and i ran in to what i think is some problems

the book says to check the voltage of the connector and that one pin should read batt voltage and others should read less than batt voltage

(with key on checking pin voltage on the isc connector harness side)
pin#1=0v
pin#2=12.43v
pin#3=0v
pin#4=0v
pin#5=12.46v
pin#6=0v

then it says to check the resistance between pin 5 and either pin 4 or 6
and it should be in the order of 30 ohm
pin# 5&4=0 ohm
pin# 5&6=0 ohm

so i had a buddy turn the key off and on so i could see if the isc cycles or not
it dose but not very smoothly. it sort of shudders into place
i check another isc i had from a known working motor and the same i get articulation but in a vibrating shuttering motion

so my question is this i guess where do i go from here? and what pins should read what?

J_HEATH · Sep 6, 2011

have you replaced the idle air control valve?

Nasty Dream · Sep 7, 2011

L train said:
so i had a buddy turn the key off and on so i could see if the isc cycles or not
it dose but not very smoothly. it sort of shudders into place

L train said:
i check another isc i had from a known working motor and the same i get articulation but in a vibrating shuttering motion

So it's a little different?

L train said:
so my question is this i guess where do i go from here? and what pins should read what?

Did you try putting the known working one in your car? That's a pretty easy way to find out if the ISC is the problem.

I don't understand, you were troubleshooting like a master and then ... YOU CAME HERE

Heh. I would have skipped all of the tests except the one where I put the working one in my car.

yokotabrat · Sep 7, 2011

When you were checking resistance, were you measuring on the harness side or at the isc? The 30ohm spec is for the isc itself. Those are the internal coils. 4 total and each of them should measure approximately 30 ohms for the tan colored iscs and 40 ohms for the black colored iscs.

The other option for you to test is another ecu. If the coils are shorted in the isc, it will damage the internal solenoid drivers. If you try another ecu, make sure all 4 coils on the isc are good before you swap ecus or you might kill the other ecu. You can also look to see if the ecu is damaged, although the isc drivers can be dead without visible damage.

L train · Sep 8, 2011

Nasty Dream said:
So it's a little different?

Did you try putting the known working one in your car? That's a pretty easy way to find out if the ISC is the problem.

I don't understand, you were troubleshooting like a master and then ... YOU CAME HERE

Heh. I would have skipped all of the tests except the one where I put the working one in my car.

haha yeah man that was the first thing i tried but it was a parts motor that "was running when pulled" crap so who knows

i guess my book kinda worded it funny and it covers 1.8 na 1990 and 91+ turbo isc and connectors witch are different so its a little confusing and i started second guessing my methods. so i just thought i would ask you guys

J_HEATH said:
have you replaced the idle air control valve?

yes just put on a new throttle body rebuild with new shaft seals( no change in symptoms)
it idles about a steady 2 grand till warm up cycle is over then hops rapidly between 1 grand and 1.5

yokotabrat said:
When you were checking resistance, were you measuring on the harness side or at the isc? The 30ohm spec is for the isc itself. Those are the internal coils. 4 total and each of them should measure approximately 30 ohms for the tan colored iscs and 40 ohms for the black colored iscs.

The other option for you to test is another ecu. If the coils are shorted in the isc, it will damage the internal solenoid drivers. If you try another ecu, make sure all 4 coils on the isc are good before you swap ecus or you might kill the other ecu. You can also look to see if the ecu is damaged, although the isc drivers can be dead without visible damage.

yes harness side. the wording in my book is a little funky.. it says ISC should read between 28 and 32 ohms between pins 5 and either 4 or 6 but then there is a picture or a guy testing the connector and his volt meter reads like 20 something ohms

ill do another ecu swap i tried my stock AT ecu (upgraded to eprom MT ecu with supporting MT equipment swaps) the stocker fired up for bout 2 seconds then died ...ill check the ISCs again i have a black and brown top. if both are found to be ok should i favor any particular one?

Lofty · Sep 8, 2011

1990 and 1991+ Iscs are a little different, the 1990 has a harness ITSELF for the ISC, if that makes sense, and the 1991+ just plug RIGHT up into the ISC.

Yes it SHOULD jutter.

However this should make things easier for you.

DmTaLoN's Idle Speed Control Test/Fix Page!

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

Idle Surge FAQ

These will all help, and more helpful articles will be on VFAQ.com

Protip: Idle air valve and ISC are the same thing.

Go for the blacktop, they are known to be sturdier.

L train · Sep 8, 2011

awsome guys thanks for all your help

ok so the ISC i swapped to is bad the brown top reads

pin
1&2=open 0 ohms
2&3=28.9 ohms
4&5=28.2 ohms
5&6= open 0 ohms

so im assuming in trying to fix the idle surge i swapped in a bad ISC and blew my drivers in my new eprom ecu when the problem was some massive boost leaks
then in hunting further i did a boost test and fixed all the leaks but at this point my drivers were already blown acting like i have not resolved the issue

my original black top that is back in the car reads (car hot)

pin
1&2=49 ohms
2&3=48 ohms
4&5=49 ohms
5&6=49 ohms

so am i correct in thinking black top good, brown top blown,probably blew my drivers?
any way to check drivers with out swapping in a new ecu. only buddy i have to swap with is running tuned link and probably doesn't want me playing Russian rulet with his shinny $400 ecu's drivers.

oh another interesting think i noticed was that when i let off the gas pedal the rpms don't drop for about 2 seconds. like the throttle switch is delayed or something ecu is supposed to cut fuel right of the bad as soon and the plate closes
i checked all of the would be obvious stuff

TPS is working in spec
throttle cable is loose
TB moves freely ( little stiff opening but closes fine)
throttle closed switch seems to be working fine fuel dose cut eventually and if wire is pulled rpm raise

could this be a bad o2 sensor? or am i just a car hypochondriac

Lofty · Sep 9, 2011

Hmm, something still doesn't seem right. I've ran bad ISC sensors in quite a few cars, never blew my ECU. So I suppose it's quite hard to diagnose this problem.

However, let's say you didn't blow your drivers.
The only way to REALLY see what's going on would be a logger of somesort, whether its MMCD or whatever, it doesn't matter as long as you can see what sensors are reading.

Regardless, something isn't right.

What is your idle at?

Last I checked, with properly working everything, when you pull off the Idle switch it wont raise the idle up. But I'd have to double check on that one.

Given there is no boost leaks, how is your CAS adjusted? That can also cause funny running issues more than anything!

Get a timing light, adjust the CAS to spec, then report back!

http://www.plymouthlaser.com/timin.htm

That will tell you how to do this!

yokotabrat · Sep 9, 2011

In your resistance measurements you say open, then you say 0 ohms. Open usually means infinitely high resistance, whereas 0 ohms is a short (no resistance). Which one did you see on the multimeter? Usually with a dead short (0 ohms) that's easily enough to overload the drivers to the point of self-destruction.

A good way to test an isc is plug it in to the harness (your good ISC) and leave it disconnected from the throttle body so you can watch it. Pull battery power for a few seconds to reset the ecu. Put the battery cable back on and turn your key to the "ON" position (not start). The ecu should re-home the isc and the result should be your isc clicking and moving for about a second or 2. If you hear nothing at all, that should be a good indicator your drivers are dead.

L train · Sep 10, 2011

Lofty said:
Hmm, something still doesn't seem right. I've ran bad ISC sensors in quite a few cars, never blew my ECU. So I suppose it's quite hard to diagnose this problem.

However, let's say you didn't blow your drivers.
The only way to REALLY see what's going on would be a logger of somesort, whether its MMCD or whatever, it doesn't matter as long as you can see what sensors are reading.

Regardless, something isn't right.

What is your idle at?

Last I checked, with properly working everything, when you pull off the Idle switch it wont raise the idle up. But I'd have to double check on that one.

Given there is no boost leaks, how is your CAS adjusted? That can also cause funny running issues more than anything!

Get a timing light, adjust the CAS to spec, then report back!

Engine Timing

That will tell you how to do this![/QUOTE

cant i adjust my CAS with gnarly idle hop. 1000 to 1500 very rapidly
i just put it to where the motor sounded healthy and gave me ok power. i don't rod it till i get this issue solved and i listen for detonation constantly. unfortunately this is my only car (RIP corolla). so i need to drive it

as far as the idle switch when its pulled off (of a car with idle hop) the ecu no longer cuts fuel to aid in engine breaking the ecu simply adjust fuel to match incoming air because it thinks the throttle plate is cracked open, for example a bad isc would allow more air than necessary for a idle of say 800 rpm. with the switch on and working the ecu will cut fuel until 1000 rpm once it hits 1000 rpm it turns on the injectors to maintain idle, with extra air leaking around the throttle plate via the Isc the car has to suddenly add fuel to achieve the correct ratio causing a sharp rise in rpm your idle switch then tells the ecu the throttle plate is closed so the ecu cuts fuel because rpms are above 1000. rpms drop ecu turns on fuel ect thus your hop cycle begins. removing idle switch will break this cycle and allow the motor to run at what ever rpm the air flow will support

but yes you are right in a well adjusted motor removing the idle switch should not raise your rpm. this is simply a means of verifying you got to much air!

i am learning alot fast with the help suggestions and info you guys give. just need to keep thinking of what it might be and figure out ways to isolate the suspected problem from other systems to 100% rule them out as a functional system until i find the nonfunctional one. I plan on developing a clear and comprehensive way of doing this and adding to existing trouble shooting pages after i figure this one out.

yokotabrat said:
In your resistance measurements you say open, then you say 0 ohms. Open usually means infinitely high resistance, whereas 0 ohms is a short (no resistance). Which one did you see on the multimeter? Usually with a dead short (0 ohms) that's easily enough to overload the drivers to the point of self-destruction.

A good way to test an isc is plug it in to the harness (your good ISC) and leave it disconnected from the throttle body so you can watch it. Pull battery power for a few seconds to reset the ecu. Put the battery cable back on and turn your key to the "ON" position (not start). The ecu should re-home the isc and the result should be your isc clicking and moving for about a second or 2. If you hear nothing at all, that should be a good indicator your drivers are dead.
Click to expand...

yes i did this test i just got another (#3) known working isc from my friend who ran it on his car. i do believe i didn't blow my drivers. i just plugged this one in and had him cycle it while i watched. it works
im sorry about the confusion with the wording. in my head 0 ohms is open. i should know better! yes one of the coils for excursion was open and one coil for retraction was open, infinite ohms

just before i came in to go to bed and check tuners i found 6 completely effed wires in the sub harness to the thermostat housing and o2 sensor some cracked burnt frayed and one wire to the o2 broken off. it was all hidden by old ass loom and gobs of electrical tape that was basically plastic. dsm lesson for today assume the previous owner was a complete boob and new nothing of cars.... double check all of his "patchwork"

ill get back to you guys with pics of the Micky Mouseness in the morning

i think this is a sort of dsm hydra problem in the process of fixing one problem i uncover 2 more. and this hop issue is hard to diagnose because its like 6 things masking each other

tkstoygsx · Sep 26, 2011

pics? and did this fix your problem

badbluething · Sep 28, 2011

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

This helped me out with my ISC problem. ^

The Top DSM Community on the Web

need ISC help

L train

J_HEATH

Nasty Dream

yokotabrat

L train

Lofty

L train

Lofty

yokotabrat

L train

tkstoygsx

badbluething

Similar threads

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds