UCF20 Warm Low Idle/Stall - easy workaround by gmacrae

By diyauto
( 2 )

3 minute read

UCF20 Warm Low Idle/Stall - easy workaround

Compliments of gmacrae @ www.clublexus.com


I got sick of my 95 LS400 stalling when pulling up after a long highway cruise. I had cleaned the throttle body, cleaned the IAC valve, replaced air filter etc etc, and the problem persisted. It definitely seems like the ecu closes the IAC valve when cruising at highway speed, but forgets to open it back up when you pull up to stop. I refused to just get into the habit of turning the a/c on when pulling up. I dont like my chances of finding a replacement ecu here that actually sorts the problem.

My fix required about 30cm/12" of vacuum hose (2-3mm i/d), and a single T piece (4mm i/d).

The aim was to feed the engine a small amount of extra (AFM metered) air, so that when the IAC stays shut, the engine is still able to feed itself enough to keep idling.

First, cut the vac hose that runs down from the intake to the power steering, insert the T piece inline, then run the vacuum hose from the T to the little unused nipple on the intake toyota conveniently left for us.

This basically increases the engine base idle roughly 300rpm thanks to the perfect size of the unused nipple. The ECU just adjusts the IAC to keep the idle speed where it should be normally. 

This also stops the 'jerk' when stepping off and back on the gas when cruising around 80km/h.

Hopefully that does the trick for the rest of you. Questions/comments welcome.

*** UPDATE - this fix is still working perfect roughly 6 months later ***

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