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Hold Power Set up for 1UZFE 6 Wire ISC


Isaac Probert
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Hi there,

trying to sort out a Idle speed problem on a 1UZ. I have set up a Hold Power system but Im still getting stuck. I turn the Key on, the ISC travels all the way in and sits there rattling on its 'stops' for a few seconds. Car starts and I can adjust the idle base map fine to get the RPM around 900. Store and turn off the engine, the Hold relay stays on and the ISC moves all the way back out and rattles like mad at the other end of travel until a moment before the Hold relay releases, at that point the ISC comes off its seat a small way.

I thought I was on top of this but the same thing happens every time, when I restart the car it idles higher then the start before. Its like its forgetting where the ISC ends up. I tried switch AUX 5 + 6 but that just makes it start with lower and lower rpm.

So I obviously am doing something wrong here, the 2nd question is can I stop the ISC rattling on the end of its stops by reducing the hold relays active time or something?

Thanks for your help

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The rattling at the end of the travel is the issue.

You will need to reduce the max and min step values so that on reset the stepper only just reaches fully open.

What should happen is at key off the stepper fully opens (but doesn't rattle at end of the travel)  and then resets to normal idle position.

Typically for a 1UZ the step numbers will be around the 60-80 mark with a max clamp of 120ish

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Thanks Simon,

That was a great help, Im not quite there though. I reduced the Min/Max clamp to 10/120.  I can get a nice 900rpm idle with the base idle figure at 85. It seems to start up in the right place now without getting higher and higher start rpm but Ive just got a little rattle still to get rid off when I shut down (as I turn the key off I still get 2 or 3 clunks from the ISC). I can remove the rattle completly if I reduce the Max clamp to 90, but it wont let me use 90 or 95 for my idle at cold temp to bring the revs up of coarse. Am I right in thinking that the Min/Max clamp is just telling the ECU how much it can move forward and back? If its the Max clamp that affects the shut down rattle, and thats getting too close to my desired base idle, do I need to move My ISC to the middle of its travel (for example) and then start again?

Thanks for the advice.

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Yes that would be worth a shot. You might find if the stepper is mostly operating close to fully open that the butterfly stop needs to be changed to keep the butterfly open more.

If you do this make sure to reset the TPS.

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