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Idle speed too high


dave88sw

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Hi,

My dad and I have just got his 3.5 V8 Defender running on megasquirt.  It was a complete kit from Megasquirtv8 loaded with a base map.  It seems to run very well, but although it idles around 900rpm on cold start (i'd guess that's about right as it's in warm up mode), the idle speed seems to increase as it warms up, ending up about 1200-1300rpm.  The target idle speed is set at 830rpm, but we've tried dropping it with no change.  We have calibrated the TPS and again, no change.

It has no IAC valve, so as i understand it, it's to be expected that the Idle is higher than usual but this does seem excessive.

The throttle flap would appear to be basically fully closed and we've checked for inlet leaks and can't find anything.

 

I should say, it's not actually been on the road yet, so no tuning has been done but it would be nice to know how we might be able to get the idle down.

Thanks in advance,

Dave

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There is a 1/4" hex grub screw on the throttle body, perhaps under a plastic cap still, that acts as a throttle bypass, use this to set the idle speed :)

Without an IAC, there is no point trying to set a target idle speed, it has no way to control the air going into the engine.

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As Bowie says - if you've got no IAC or PWM valve fitted then the ECU has no direct control of idle speed. TPS calibration has nothing to do with it either, that's just giving the ECU a reference for what's zero throttle and what's full throttle for a few minor enrichments or flood-clear mode at startup.

Mixture & timing will have some effect on idle speed but if you haven't found and wound in the idle bypass screw that's thing #1.

I'm assuming with no idle valve fitted you're blocked off the air passages that would usually be used by the valve?

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