Very low idle when warm, 1990 1UZ

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American Locomotive

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Hey guys, I've got a relatively low miles (~100,000) 1990 1UZ installed in a Jeep Cherokee with the Jeep AW4 automatic installed behind it (the AW4 is the same thing as an A340E, but uses an external transmission controller).

It starts up fine and great, high-idles at ~1200 RPM cold, and as the coolant temperature comes up the idle speed drops. Once it hits full operating temperature, the idle drops to around 500 RPM. This is rather annoying, since alternator output at 500 RPM is low, and it tends to vibrate the vehicle a bit, especially when you put it into gear.

Any ideas what could be causing the low idle speed? The IACV works perfectly and there are no vacuum leaks. I was thinking about possibly jumping gear selection pins to make the computer think it was in park/neutral?
 
Most 1uz I work on have a low idle between 550 and 625 depending on the ecu . When running with a different trans control I normally wire as if it's a manual. If the shift select switch isnt wired the default mode is park/neutral.

How is the gear selection wired into the 1uz Ecu now? Have you connected a scan tool to monitor the engine?
 
No gear selection is wired at all. Looking at the wiring diagram, leaving all the transmission gear selection wires unhooked is the same as "Drive". Park/Neutral short the NSW and STA lines together. "Drive" isn't connected to anything. 2, Low and Reverse each have their own wires going to the computer. Here's a picture, as you can see the "Drive" connection only goes to the dashboard light and nothing else.

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We don't have a scan tool capable of hooking up to the diagnostic port on the 1990 Engine. We did use some software we found that can monitor live-data through a serial port connected to the engine, but it's buggy.
 
Sorry you are correct. Default is drive and this should be fine. It was a long day on another conversion. Toyota never intended this engine to be revved high in park or neutral. If you are really concerned there are tricks to artificially increasing idle speed. Are you running the power steer idle up?
 
And good data is the best way to check things even if it's a little primitive in early engines. Wire in the underdash diagnostic and find a scan tool. I'm doing one today.
 
Sorry you are correct. Default is drive and this should be fine. It was a long day on another conversion. Toyota never intended this engine to be revved high in park or neutral. If you are really concerned there are tricks to artificially increasing idle speed. Are you running the power steer idle up?
My main problem is the idle speed is so low, the alternator is barely putting out any power. That and sometimes it almost stalls putting it into gear. I never started the donor car (engine came from the JY), so I don't know what a 1990 1UZ should idle at.
 
I think I might try putting it into "Park" and seeing if the idle comes up. Does anyone know if there is a difference into how the computer handles timing/fuel in "Park" vs "Drive"?
 
Are you running the powersteer idle up? If not its possible to bleed some air into the fitting to increase the idle speed. I try not to do it but it does work when done correctly.
 
i also am having this issue with a low idle . I deleted the power steering vac supply , which hasnt helped. I was considering wiring an aftermarket idle up solenoid like for the chevy 350s but they work inline with the throttle linkage on the chevys where as i have a throttle cable. I will say the low idle sucks especially with the A/C running .

My 1uz is manual swapped into a cressida ( so not factory setup)
 


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