2G Unplugged IAC = no difference

[swnkylaxplyr]

I've been dealing with a bad idle since I bought my 98 GSX in July. Today I tried seeing what would happen if I unplugged the IAC - no discernable difference. Shouldn't there be?

 

[miller97tsi]

not to sure on this one, i had the same problem a while back ago i just took the iac out cleaned it good and just replaced it. problem solved but i did this while the car was turned off.

 

[swnkylaxplyr]

What did you clean it with?

 

[clean96GST]

Is this the same thing as the ISC?

 

[davidalindsey]

Is this the same thing as the ISC?

yes.

Replacing the ISC

 

[steve]

The ISC/IAC doesn't move if you unplug it, it stays exactly where it was.

 

[miller97tsi]

i just cleaned it with a toothbrush and some brake cleaner let it dry and reinstall it.

 

[steve]

Before you put it in the TB connect it up and have somebody turn the ignition on. It should smoothly move in out and in as the ECU recalibrates it. If it just shakes it's bad.

You should also measure the coils resistance and make sure it's not shorted or open. There are four coils. pins 1 and 2, pin 2 and 3, pins 4 and 5, and 5 and 6. (the center pin in each row is common to both coils. Each should read between 28 and 40 ohms. It you measure any shorts then you'll need the ECU fixed to replace the blown driver the shorted coil blew.

 

[swnkylaxplyr]

Okay thanks I'll give it a try

 

[snowborder714]

Here's a website that describes what Steve was mentioning about testing it.
http://web.archive.org/web/20100815101158/http://dmtalon.v8eaters.com/ISC.html


Here's a video of a properly working ISC.

YouTube - DSM ISC

 

[swnkylaxplyr]

My IAC does move in and out when the ignition is turned on, so thats not the cause of my problem. Thanks guys.

 

[steve]

So define "bad idle".
Have you checked your IPS inside the TPS? If it's not closing the ECU won't know to manage the idle.

 

[swnkylaxplyr]

So define "bad idle".
Have you checked your IPS inside the TPS? If it's not closing the ECU won't know to manage the idle.

No I have not, how would I go about doing that? My idle "rolls" - it fluctuates from about 600~1100. Its not like a car's idle with cams, its slower, but keeps going up and down without ever steadying, even for a bit.

 

[feardafish]

sounds like idle surge. Check for boost leaks? is your BISS backed all the way out?

 

[swnkylaxplyr]

sounds like idle surge. Check for boost leaks? is your BISS backed all the way out?

I actually put the BISS all the way in without getting the idle to around 750 rpms - I have it set to around 1k right now. As for boost leaks, I've been checking; repaired PCV valve+installed check valve, replaced EGR gasket, both throttle body gaskets and BISS screw+o-ring. Still hear a good(bad?) amount of leaking, so I'm guessing shaft seals.

 

[swnkylaxplyr]

*bump* Any reason why my idle would be steady after beating the crap out of my car tonight? I ran it pretty hard, and when I came to idle it was steady at 1k, which is what I set it at because anything under that is horrible.

 

[steve]

No I have not, how would I go about doing that?

Reposted to save you from having to find it.

2G's critical TPS adjustment is the Idle Position Switch that's part of the TPS.
(2G TPS pins are 1- 5v, 2- TPS output, 3- IPS output, 4-ground)

You place a .177" feeler guage between the stop screw (fixed SAS) and the throttle pulley to open the butterfly and then adjust the TPS right to the point where the IPS (pins 3 and 4 on the TPS) switches from closed (0 ohms) to open (infinite ohms). Then you verify that the TPS (pin 2 and 4) reads between 0.4 and 1V while the feeler guage is still in place. Anything in that range is ok as long as the IPS is adjusted correctly. It it's not correct you need to check that pin 1 is about 5v and pin 4 is grounded. If they are correct then the TPS is bad.

There is no way to adjust the TPS voltage independantly of the IPS on a 2G. Trying to correctly set a 2G TPS by voltage will only work by dumb luck.

I actually put the BISS all the way in without getting the idle to around 750 rpms - I have it set to around 1k right now.

I ran it pretty hard, and when I came to idle it was steady at 1k, which is what I set it at because anything under that is horrible.

The ECU is programmed for the idle speed. You can to changed that programming in order to change the idle speed. Getting a different idle is only possible by driving the ISC out of range to where it can't correct or by the IPS malfunctioning so that the ECU doesn't know the throttle is closed and that I should be controlling the idle.

If you can won't idle below 1k and you don't have some big cams you need to resolve that problem too.

 

[swnkylaxplyr]

Steve- thanks for the write-up. Adjusted the TPS/IPS and there have been noticeable improvements, but my idle still isn't awesome by any means and I can't get it to stabilize at ~750. While taking out my IAC, I noticed a broken strap on my throttle body behind my IAC that seems like a ground. I know there is a ground on the throttle body and this seems like the only thing like a ground so I'm guessing my ground is broken. I've heard this can cause problems - if this is indeed my ground is there any way to fix it?

Also, I took my IAC out to test resistance on it and couldn't get anything but 0. Am I doing something wrong or is it shot? I checked resistance on my TPS just to make sure that the multimeter was working and it was so it seems to be the IAC itself.


Also, it may be unrelated, but could this broken ground be the reason my battery and brake lights are always on? I checked the battery and changed the alternator multiple times with no difference so I'm guessing I have a bad ground.

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[steve]

Because the IPS is inside the 2G TPS I don't think there is a throttle body ground strap like on a 1G. It gets it's ground from the same connection the TPS uses. The strap in your pictures is just that, a strap to support the wires to the TB, not a ground.

Are you getting a 0 ohm reading measuring the ISC/IAC coils or the same reading you meter makes when the probes aren't touching? You want to be measuring the resistance between pins 1 and 2, 2 and 3, 4 and 5, 5 and 6. If they are shorted (0 ohms) then the ECU drivers are also likely blown.

 

[swnkylaxplyr]

No, without touching, I was reading 1, but when I tried to test resistance of any of the coils I would get 0.

If I get an ECU out of a junked car, does it need to be reprogrammed and secondly; is a shorted/fried ECU common enough of a problem that I'd want to get a new/reman one?

 

[steve]

Unlike later cars there isn't an car specific reprogramming required. You just need the same part number ECU.

 

[swnkylaxplyr]

Okay what if I wanted to use this opportunity to justify buying an eprom ecu? Would the part number difference be an issue?

 

[steve]

The only 2G EPROMS are out of 95 cars. There are functional differences between the engines so you have to swap the plug wires. The ECMTuning site has details for people running ECMLink on a 95 ECU in the later cars.

The 98/99 ECUs have flash memory so they can be modified using the openport 2.0 cable. See the threads on ceddy mods for details.

 

[ctsellersjr]

did you ever figure out what the problem was?