1JZ "hunting" at idle

[BlackMKIII]

It started with a low idle about 2 weeks ago, then about a week ago it kicked up to normal. Then it started climbing to 1500, then 2000 one day. Now it's fluctuating between 1400 and 2100, and floats up and down at about one cycle per second.

At first I thought it would be the idle speed motor, but unplugging it had no effect. I checked the voltage on the throttle position sensor and saw it a bit high, so I adjusted the TPS. It fixed it for about a day, then it started again.

I can get it to idle normal for a single drive cycle if I unplug the TPS before starting it. However, if I start it with the TPS connected, it won't idle right. I thought it might be a bad TPS, but testing it both on and off the car yields normal electrical readings.

Anyone have any ideas?

 

[OneJSupra]

Check the ISC to make sure it isn't stucked open and check for vacuum leaks. Try to reset the ecu also.

 

[Cya]

If nothing changed then its probably the iscv. You can plug it and adjust your idle speed screw.

 

[BlackMKIII]

Check the ISC to make sure it isn't stucked open and check for vacuum leaks. Try to reset the ecu also.

I checked all the major vac lines. No leaks detected. I mentally ruled out the ISC because it's a fast hunt, not a slow rise and fall. The thing that's really odd is how perfect it runs if I start it with the TPS unplugged.

Also, where exactly IS the idle speed screw on a 1J?

 

[RockPaperSwoRD]

its that little protruding screw that contacts the throttle spool when its closed. if you screw the screw in more, then the throttle will open a tiny bit, should be enough to make it idle right.

mine is also having retarded idling issues, i tried unplugging the isc and it would idle at 1000rpm, then when i plugged it back it would idle at 300 -_-