High Idle :/ (1 Viewer)

Joined
Mar 29, 2021
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Ogden
Hello all, I'm curious if anyone could answer a question for me on the topic of strange idling.

Issue started like this, one night like every other it idled warm in park at ~800 then the next day it started cold at 1000 and when warm idled in park at about 1200. We originally thought it might be an issue with the acsd but it appears to have already been deleted by a previous owner. We then tried looking for a vacuum leak.

We couldn't locate a source for a vacuum leak so we tried resetting the ecu to see what would happen. Started at 800 but after driving to work it idled at around 1400. Reset the ecu again and back down to 1200. We also checked to see if turning on the ac would change anything, and no change in the rpm.

Thank you for your time.

Model is a '91 Hzj77 for reference
 
Joined
Jul 22, 2003
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18,375
Location
Perth Western Australia
The spring under the accelerator pedal has lost tension. I've been through this once and fixed it straight away after hearing of US owner of a 60 series with the same problem.
How do you reset the ECU on a 1991 1HZ?

Diesels are not affected by vacuum. They make their vacuum via the vacuum pump and is not attached to fuel injection(except to make it idle faster when you turn the ac on).

If its not the spring I mentioned, it could be in the fuel pump. I would also have a closer look at the AC vacuum idle up
 
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Joined
Mar 29, 2021
Messages
4
Location
Ogden
Thanks Cold Taco I fiddled with the knob and it definitely helps but the idle adjustment screw has about a .150 inch gap between it and the idle arm thing (can't remember terminology). I checked the spring under the accelerator and its still strong. AC does not blow cold and compressor is not engaging. Pic of idle position and diaphragm that's connected to the idle up solenoid.
20210329_234821.jpg
20210329_234738.jpg
 
Joined
Jul 3, 2004
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4,017
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Anchorage, AK
The idle up knob to the right and low of the steering wheel only goes to the accelerator pedal under the dash by the firewall. It pulls back the go fast pedal, so either increasing gas or lessening gas. You have to look at it to see how it works. This knob doesn’t do anything passed the firewall. Don’t know if you already knew that.
 
Joined
Aug 5, 2014
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396
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DFW, TX
Based on your pictures, You should definitely be looking at the spring(s) that will return your throttle back to idle. It should be resting on that screw in your picture above. Your diagnosis can't continue very successfully until you can ensure your throttle is resting in the same spot every time.

If that gap is just there from you turning the throttle adjustment up, then ignore my statement. Just endure that under normal conditions, your throttle link is resting on the idle screw.
 
Joined
Mar 29, 2021
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Ogden
Hey guys just want to say thank you for helping me, I'm really new to cruisers and diesel so every bit helps. I checked the throttle linkage and the springs seem to be in order, but it really does not want to return to the idle position. What mechanisms could cause it to stick and not return to idle?
 
Joined
Jul 3, 2004
Messages
4,017
Location
Anchorage, AK
Probably if the idle up knob is turned in too far since it would limit the throttle from moving far enough in the direction it needs to go. Not home for a while but I think if you turn the knob left it should reduce idle speed. Turning to the right increases idle speed
 
Joined
Mar 29, 2021
Messages
4
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Ogden
Oh my goodness, you guys just occam's razored the hell out of this. All I needed to do was turn the knob till it was loose and bam, sits flush against the screw now. :D You guys are the best, might need to do some reading so I don't inadvertently cause me issues.
 

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