Toyota 8FGCSU20:
Seeking at Idle

Having a problem with this lift Idling... No Fault codes

I have tried adjusting and cleaning the accelerator pedal potentiometer and throttle body with no change.

Have found if I unhook the hose coming off the intake pipe between the air cleaner and TB it cures the problem. This hose runs off the intake pipe across the top of the engine into a square shaped box that looks like an charcoal canister on a automotive application that is located under the Regulator/Vaporizor assembly. I do not see a sensor in this "box" but on the top of it there is a hose that runs to the LP Regulator/Vaporizer. The thing is this hose doesn't release any pressure or vacuum but if i picks up any vacuum or pressure from either blowing into it or creating vacuum it stalls and dies.. Any ideas to what is creating this problem im having or what that hose and box's Function is?

Thanks in advance help is much appreciated!
  • Posted 6 Feb 2014 11:32
  • Discussion started by TNMobileTech
  • Tennessee, United States
Showing items 1 - 4 of 4 results.
Thanks Liftmech for your answer ,it helped me with the same problem I was having with my forklift.
  • Posted 21 Jul 2021 03:26
  • Reply by Bobby_Brown
  • South Carolina, United States
Thank you for the help guys I will be trying your suggestions today and hopefully get this thing right.
  • Posted 6 Feb 2014 21:20
  • Reply by TNMobileTech
  • Tennessee, United States
The plastic "box" near front of LP regulator is a "baffle chamber" (aka resonance defeat chamber). Its purpose is to provide a clean, dust free pathway for the regulator secondary diaphragm to be able to move freely when it needs to operate. The hose runs to the air cleaner so any incoming air will not be dusty. The baffling effect is so the diaphragm is not likely to react to induction vacuum pulses originating at the air pipe the hose connects to.

The valve on the side of the mixer/throttle body is not an air valve. It is a fuel valve. Toyota/Aisan call it the fuel control motor.

I have found 2 main causes of hunting/surging at idle, AND a flat spot or hesitation when you press the accelerator on the 8F trucks.

The tamper resistant cap covering the idle fuel adjusting screw on top of the regulator needs to be removed so the idle fuel screw can be adjusted slightly. Often you only need to turn the screw CCW about 1/2 to 3/4 turn and the surging will go away.

The second thing that can have a profound effect on idle and take off is a gummy mixer/throttle body.
We remove the mixer/TB and clean out the main throat plenum, throttle plate, and the fuel control motor tip and passages.
I recommend that you orient the mixer so that the throttle plate operating shaft coming out of the throttle motor is always "up hill" while you are wetting and scrubbing the carbon deposits out with a toothbrush and spray carb cleaner. Keeping the throttle shaft up hill will keep carb cleaner from leaking past the throttle shaft bushing and into the TS motor case.
  • Posted 6 Feb 2014 15:56
  • Modified 6 Feb 2014 15:59 by poster
  • Reply by L1ftmech
  • Tennessee, United States
Have you drained the oil out of the regulator? I have run into a couple of problems with the idle and have found either the air valve on the side of the carburetor gummed up with oil or the lp regulator n/g. The air valve is on the side of the carburetor where the lp hose is, it is held in with 2 screws. Take it out and clean it. The best way to diagnose is to have the hand held and get readings.
  • Posted 6 Feb 2014 11:48
  • Reply by rogeriwt
  • Massachusetts, United States

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