1G weird headlight idle issue

[red talon]

So I have this issue were my car idle's a bit high (950-850) rpm but when I turn on my headlights, the rpm goes down to about (750-700) which is normal and it only does it when I have the lights on. I have tried just the pop up'w/out the lights and does not effect it. So any suggestions or help would be very helpful. Thank you

 

[steve]

Sounds like the idle circuit isn't working correctly.
Start by checking that you have a good ground to the throttle body and that the IPS is pulling the green wire from the ECU to ground when the throttle is closed. Make sure you have a 90 ECU in the car since the later ECU switch the pin location for the IPS signal on the harness.

Then check the ISC coil resistances. All four coils should read about 28 ohms. If any measure below 28 ohms the ISC may have damaged your ECU. If they read over the ISC won't damage the ECU but it may not step correctly.

Once the IPS and ISC are tested it's time to clean the throttle body and then readjust the BISS screw. The ECU is programed to hold a 750 rpm idle, the BISS needs to be adjusted so the the ISC is correctly positioned and the idle speed set. You need to ground both the timing check connector under the hood and the mode pin on the diagnostic connector to adjust the BISS or use a datalogger to set the ISC to about 20-30 steps at 750 RPM, while fully warmed up and all accessories off. This give the ISC enough range to increase/decrease the air it bypasses to control the idle.

There are threads here on each of these steps and it's covered in the factory service manuals which you should have a copy of.

 

[red talon]

Thank you so much. I will do this once I get my first pay check. If i need a data logger. I will get link. But thank you again