ISC/IAC testing questions and issues (Merged)

[98gsxturbo]

Hey guys well i just got done testing my ISC to see if it was messed up or not. I looked up some instructions on the net and followed them, and i got the following readings on my ISC in Ohms. This is a basic diagram of the pins in the ISC that I measured..

1 2 3
| | |
| | |
4 5 6

Pins 1 & 2 = 27.4 Ohms
Pins 2 & 3 = 27.5 Ohms
Pins 4 & 5 = 27.0 Ohms
Pins 5 & 6 = 27.4 Ohms

Where my instructions were it says that acceptable readings were anywhere between 28 and 33 Ohms. I'm a bit out of that range. Should I consider my ISC shot and replace it? If any of you guys out there with a shop manual can look this up to verify it that would be most helpful. thanks!

 

[Beemer]

That's about average, and you can't be sure that your ohmmeter is calibrated correctly either. Actually though, I thought there was a variance in resistance between the steps...I remember seeing something in the vfaq that had the listings for acceptable resistance...ah damn, it was voltage i think, off the 3 steps. Check the vfaq to be sure. I have found that most ISC problems are due to the plunger being dirty where it seats. Try some rubbing alcohol on the tip and the seat to clean them up a bit and soften the tip some. Helped me anyways.

 

[MitchTSIAWD]

I was testing my ISC so i unbolted it from the TB and left it connected to the harness, and i had a buddy turn the car from ACC to ON 2 0r 3 times. The ISC did move but does any one know how much it is suppose to move roughly, an idea. Because it didn't move much maybe like 1/4" at the most is this a good working ISC.

I have an extra one that all it does is vibrate, I know that one is shot.

 

[teme]

Yeah it shouldn't move much....
just when u turn the power on it goes littlebit up, and when u turn power off it goes down..

 

[boostedinaz]

That's only part of the way to test an ISC. You also need to test the OHMs between the points in the connector. That will tell you if it is bad or not. Even if it says it is in spec the car may idle funny and then it should be replaced. Here is a very informative thread. In it there are links to see how to test the ISC and places you can buy them from.

http://www.dsmtalk.com/forums/showthread.php?s=&threadid=111009

Michael

 

[Gabe92RTTT]

Hey all,

I am having issues with my idle when my A/C is turned on; it drops from 800 to 500. I have searched and searched and only one person successfully fixed it on my search results and it turned out to be his alternator. I am going to go have my alternator checked at AutoZone in a bit but i doubt it is that because its fairly new. My battery is ok as well.

I don't have any other idle issues, no surging and base idle is set fine. I have no intake leaks either. I tested the ISC motor between pin 2 to 3-4 as well as pin 5 to 4-6 and they both gave me readings of 36.x Ohms (car was warm). The service manual states it should be between 28-33 Ohms. What does this mean?

Ok, found the VFAQ and it explained exactly how to test it and to test while cool. I will go back and get better numbers once it cools.

Ok, now that the car was cool the test came out ok at all pins around 33 ohms.

So what can be causing my idle to drop when the A/C turns on?

 

[jrpmp69]

I think that is normal in all cars due to the a/c putting a load on the engine to run the a/c compressor.

 

[steve]

So what can be causing my idle to drop when the A/C turns on?

There is more the the circuit than just the ISC. The idle position switch has to be closed and the ECU ISC circuits need to be working. Since on of the ISC traces runs right under the C106 capacitor any leakage will usually take it out and often IC105 with it.

Steve

 

[Gabe92RTTT]

Ok, could a bad FAIV cause this to happen? I know mine is bad because the car idles at 600RPMS when it is first started. Can these two be linked?

 

[rad]

FIAV adds some extra air untill coolant gets hot. It's not controlled by any logic, it has it's own air passage. ECU>ISC controls your idle, it lets more air in when AC/power steering comes on, etc. Don't worry about a few ohms off on the ISC, just make sure ALL windings are in the range. If that checks out probe the ECU, like Steve says.

 

[Gabe92RTTT]

Alright I tested the ISC using a 6 volt battery like instructed on v8eaters vfaq. in his faq it says ,"If there is no movement or vibration from the motor, then it is bad ." I first tested the ISC on the car and couldn't hear or see any vibration so I took the ISC off and tested it. It twitches back and forth a tiny bit, barely noticeable. How much is this thing suppossed to move?

 

[steve]

It twitches back and forth a tiny bit, barely noticeable. How much is this thing suppossed to move?

About that much. Without driving the coils in the correct sequence the pintle isn't going to move in and out. It's not a DC motor like the one found other cars.

Your done testing the ISC. You were done after you measured the coils. I've yet to see one with good coils that didn't work if the ECU was good. Make sure your IPS is working. If it's good then it's time to pull your ECU and have it checked or swap another know good one in and see if the AC idle up starts working.

Steve

 

[Zacksdsm]

Can the ISC cause a misfire?
I tested it and it has no resistance on any coils...
Could this alone cause a DSM to fail emissions?

 

[steve]

I tested it and it has no resistance on any coils.

Define "no resistance"? Does that mean infinite or zero ohms? Either case is bad but zero ohms is much worse because it causes the drivers in the ECU to blow.

Steve

 

[Zacksdsm]

I tested with an multimeter and the needle went all the way to the right as if I just touched the prongs together.. I will test again when I get home.. Thanks

 

[steve]

Make sure the meter is set on the right scale for the expected resistance. Since the ISC coils measure about 28 ohms normally a scale that measures to 100 or 200 ohms would be correct. If you set it on a scale that measures 1000's or 10,000's of ohms the needle is going to be very close to the zero and you won't get a good reading.

Steve

 

[Zacksdsm]

Good point. I double checked and the multimeter reads at x1k for ohm and is my only option.

But I tested it again and it reads exactly as if the prones are touching together. The needle goes in the same spot it read nothing.

Has this happened before on these ISC?

I guess I could find/get/buy a multimeter to test but would rather not incur the cost at this time...I'll do what I have too..

 

[steve]

Has this happened before on these isc?

It's somewhat unusual for all four coils to be shorted but it's possible. If that is the case you need to pull your ECU and look for burnt drivers. They're the black 8 pin inline IC's and there are a bunch of them but only two of them are for the ISC. You'll need a new ISC too.

Steve

 

[Zacksdsm]

All coils read the same. It is possible that my cheap radio shack multimeter is not reading it. But the needle is in the exact spot as if the prongs are shorted. Could external bov dump cause this?
Or could this lead to a cylinder #1 misfire?...because this is my problem with my car. The engine codes is bad isc and misfire in #1

 

[Zacksdsm]

Going by this article...
http://www.dsm.org/how-tos/tttt/tttt3.html

I unplugged the isc and it did absolutly nothing. The rpm's did not change at all nor did the behavior of the idle.

Any thoughts there?

 

[steve]

I haven't read that in many years so help me by pointing out where in it you get the idea that unplugging the ISC is going to make any difference. Our ISC's don't do anything special if you unplug them. They just stay positioned where they were positioned not retract to home or something that a Honda might do.

Depending on which coil or which drivers in the ECU are bad I've seen the ISC be totally dead, only able to step out consistently, or only be able to step in.

Since the ECU first opens the ISC quite a bit for starting and then quickly close it down once the engine fires and once the FIAV starts closing the ECU then opens the ISC a little, you get a bunch on interesting failure symptoms. If the ISC is stuck open (all the way or just a bit too far) you get idle surge. If it's stuck closed the engine dies once it's warmed up coming to a stop and sometime times between shifts.

 

[Zacksdsm]

Forgive me if im mistaken the isc with the idle switch...


FROM THE ARTICLE------

My car has an idle surge
While the car is surging, smell the exhaust (ie. hold your hand in front of the exhaust pipe for a few seconds, smell your hand) It should smell like partially burnt fuel (rich).
Pull the connector off the idle switch. The idle should stabilize somewhere above 1500 RPM. Smell the exhaust again, it should smell like a proper mix, ie. no odor. If you have access to the O2 sensor test connector under the dash, you can confirm a proper mix by checking it with a DVM. The O2 sensor normally outputs a value between 0 and 1 volt. (0=lean, 1=rich)
NOTE: Do not trust the O2 sensor output unless the engine RPM is steady. The lag time in the sensor makes it useless for correctly reading a surging engine.
If the exhaust smells fine and the O2 sensor is sending reasonable values, go to step 2.
If the exhaust still smells rich or lean (the vapors sting your eyes), think about getting an emissions inspection and suspect that you may have a bad oxygen sensor. If you'd like, you may follow the instructions for inspecting the O2 sensor as found in the shop manual.

And it goes on in the article.....

 

[steve]

I wish I remembered when that was written. It may predate 2G's.

Which car are you having problems with? You profile looks like you might have two, a 95 and a 90. I've been guessing your 2G since a 1G can't throw either of those codes.

The Idle Position Switch on a 1G is on the back of the throttle body, next to the throttle pulley. On a 2G it's inside the TPS and difficult to disconnect. Unplugging the IPS fools the ECU into thinking that the car isn't idling and so it doesn't run the tests that trigger idle surge.

Since you measured the ISC coils and they were all shorted, there's no way to know where the ISC was positioned when it last worked. If the car is surging it likely too far open and like I said before, if your ISC coils really are shorted then your ECU is going to need repair work before a good ISC will operate.

I can't say what the deal is with the misfire error.

Steve

 

[Zacksdsm]

Working in the 2g. Well I think the ISC is ok but hard to tell as my analog multimeter is not very accurate. It seems to read a sliver of resitance. The person I bought the car from said he has no clue about a misfire and he had the head rebuilt in November and in Oct. he passed emissions no problem. At first I though it was the head being milledout of spec causing timing to be off. But I spent a whole day resetting the timing and it runs exactly the same with the misfire. Still has plenty of power just no torque till the turbo spools.

I was going to try the battery test on the ISC but I don't see how the ISC would cause a misfire which was one of my questions in one of these threads.

Also can fouling cause the ecu to think the engine is misfiring? If so maybe I need to look at my injector seals?
The exhaust smells of raw gas...

 

[cevic]

Guys, I know the VFAQ site talks about it. But I have just heard a different version: "You check the resistance of the isc motor coil from the plug that goes into the isc. Then you apply 6v to the motor itself. That's how you test the isc. "

The question is: Should I check the resistance on the plug that goes to the ISC or the ISC motor itself??