Idle loping slightly

[napajs13]

I was wondering if anyone knows what the readings off the isc should be when logging? I know I need to test my TPS cause I'm pretty sure its out of adjustment. I was logging and saw that my ISC was at 0%, so I'm thinking it either doesn't work or I have something out of adjustment. What does the isc work off of as in sensors? Does it read off of the tps and the closed throttle switch? Also, on a cold start, the idle is not being bumped up. Any info would be great. Thanks!

 

[Street Faze]

Cold start issue might be the FIAV on the bottom of the throttle body, sounds like it may be closed all the time(better then being stuck open trust me). As far as fixing it i'm not sure how it comes apart once its off the TB. You could replace it, i assume it wouldn't be much. Overall it wont hurt anything, you'll just have to feather the throttle until it warms up a bit.

 

[steve]

I was wondering if anyone knows what the readings off the isc should be when logging?

I know I need to test my TPS cause I'm pretty sure its out of adjustment. I was logging and saw that my ISC was at 0%, so I'm thinking it either doesn't work or I have something out of adjustment.

What does the isc work off of as in sensors?

Does it read off of the tps and the closed throttle switch?

Also, on a cold start, the idle is not being bumped up. Any info would be great. Thanks!

The ECU drives the ISC. The ECU uses the IPS (closed throttle switch), TPS, ECT, RPM, and VSS for the deciding where to position the ISC pintle.
The Coils in the ISC and the drivers in the ECU work together to step the ISC pintle. If one of the coils in the ISC shorts out it can blow the driver in the ECU so if you ever measure a coil < 28 ohms when testing you need to make sure the driver is still good.

At idle at operating temps, with accessories off, the ECU is programed to maintain a 750 RPM (DSM) or 800 RPM (GVR4) idle. It will move the ISC in or out to try and maintain this (it also varies the timing to do so). If your logging 0 steps then the ECU has tried to lower the idle speed and has driven the pintle all the way closed. It should be reading 12-30 steps.

The BISS sets the base idle speed by adjusting the baseline air bypass arounf the butterfly. The ISC and FIAV then modify the amount.

Fast idle is controlled by the FIAV in the Throttle Body and the Engine Coolant running through it. It's open when the coolant is cold and closes as it heats up.
If you have disconnected the coolant lines to the FIAV it's stuck open all the time and provides too much bypass air. If it's blocked off then the ISC is the only addition and it really doesn't have enough capacity to get a good fast idle.
While starting the ECU opens the ISC up almost all the way and then once it starts ramps the ISC position down based on RPM and ECT (engine coolant temp).

The only positioning feedback the ECU has from the ISC is changes in RPM so it really doesn't know the actual position. Each time the ECU is powered up it steps the ISC in and out to insure it's starting in a known position (by stepping farther that is possible in each direction) There are youtube videos of the ISC doing rehoming and is the way to make sure the ISC is operating correctly.

 

[napajs13]

Thanks again Steve for clearing it all up for me. I will test it as soon as possible.

Update: So I tested for continuity and found that it was open between 1 and 2. I guess I need to find one and then go from there.

 

[steve]

Go buy a new black plastic one. They run about $80 and don't seem to fail as often as the old metal cased version.