1G ISC wiring

[Anthony Boni]

Hello,

I have a 90 TSI with a 91+ throttle body. I'm having many issues with my ISC position in DSM Link V3. It reads 120 when the car is cold but rapidly descends to 0 and stays there. I cannot put the car in "ISC adjust" mode because the car idle surges like mad and eventually dies. I'm running speed density, have verified I have ZERO vacuum leaks. I've verified base timing at 5* BTDC. Car idles pretty consistently @ 850-950 RPM when ground pin isn't grounded in Link. I've ran two new ISC motors and they all ohm tested good. Sent my ECU to ECMLink and they fixed a trace but otherwise stated the ECU operated correctly. Only thing left is the harness wiring for the ISC. Can anyone give me a hand in troubleshooting the wiring from the ECU to the ISC pinouts? I've looked for a guide on this but couldn't find anything. This is really starting to kick my a** and I could use some help.

 

[steve]

Did you swap the two pins when you make up the cable to connect the 91+ ISC?

The ECU can only report what it thinks the ISC steps are not the actual position and since the ECU has driven the steps to 0 it's likely that the pintle hasn't closed off the ISC bypass.

What about the coolant connections for the FIAV, still hooked up?

 

[Anthony Boni]

Did you swap the two pins when you make up the cable to connect the 91+ ISC?

The ECU can only report what it thinks the ISC steps are not the actual position and since the ECU has driven the steps to 0 it's likely that the pintle hasn't closed off the ISC bypass.

What about the coolant connections for the FIAV, still hooked up?

I have not swapped anything. I bought it like this and wasn't aware the wiring was different between the two throttle bodies. As for the coolant connections to the FIAV, I've re-routed those back into the heater hose and capped off the FIAV nipples.

If this helps, I've plugged in the ISC motors and removed them from the throttle body. All they do is vibrate.

 

[steve]

With the FIAV coolant piping unconnected the FIAV will never close leaving an open idle air bypass (vacuum leak). Removing the ISC is the same but worse. The only way any of that would work is if you removed and capped the bottom of the TB.

If you look at the wiring diagrams you'll see that between 90 and 91 the wiring of the ISC coils changed, it's something you have to address when you make up the new connector.

 

[Anthony Boni]

With the FIAV coolant piping unconnected the FIAV will never close leaving an open idle air bypass (vacuum leak). Removing the ISC is the same but worse. The only way any of that would work is if you removed and capped the bottom of the TB.

If you look at the wiring diagrams you'll see that between 90 and 91 the wiring of the ISC coils changed, it's something you have to address when you make up the new connector.

Even with a bypass plate? I even did the "free mod" to close the FIAV by removing the water plug, compressing the spring, and re installing the water plug. And okay that's good to know, I'll look up a wiring diagram and see if this wasn't already accomplished.

 

[Dsm panda]

You need to swap the black and white wired in the harness make or the pins at the ecu if not it will idle at like 2k rpm.

 

[Anthony Boni]

You need to swap the black and white wired in the harness make or the pins at the ecu if not it will idle at like 2k rpm.

Mine idles fine, I'll have to make sure it wasn't already swapped.

 

[Dsm panda]

I would advise checking over everything on a new car maintenance is key.