Need some help with a bizzare 2F carb problem

[msapers]

Hi all, I have a stock 1976 FJ40 with the stock carb. The carb was rebuilt within the last few years, it runs good and just passed CA smog.

Now for the problem: The throttle sticks BUT, it is speed sensitive. When driving, the throttle will stick causing the engine to run at about 1800 rpm. It continues to stick until you slow below 10 mph, at whick point the throttle pedal clicks back into the normal position.

No matter how much I dick with it, the throttle will not stick unless the truck is moving above 10mph and will not unstick unless it's moving below 10 mph.

I've confirmed that it is speed specific in the following ways:
1. Brake and clutch together (normal stop) Throttle releases at 10mph.

2. Brake only. Throttle releases at 10mph

3. Nudged the trans into neutral and let the truck roll to a stop with no brakes. Throttle releases at 10 mph.

The cable, pedal, pivot points and linkages all are lubed and move freely and smoothly. The manual choke is operating properly. There is no aftermarket cruise control installed.

Because I can't duplicate the problem with the truck stopped, I can't diagnose it. Any help would be much appreciated.

 

[subzali]

Check your high idle screw adjustment. It may be that the emissions computer is forcing your engine into high idle but the idle is set too high so it's bothersome. Do you have an FSM?

 

[Pin_Head]

Mis adjusted throttle positioner? The job of the TP is to keep the idle speed above about 1000 RPM until the speed drops below 10 MPH to prevent backfiring during engine braking. Manually set the TP on and back the screw off to 1000 RPM.

 

[msapers]

Ok, that sounds like the problem. Where is the TP? The only wire I found going into the carb is at the base of the float bowl and disconnecting it didn't change the symptoms.

 

[Pin_Head]

The TP faces the fires wall. It is a lever with a screw tip at the bottom that is vacuum actuated by a vacuum pot on the US driver's side of the carb. Losen the screw to lower the speed.

 

[msapers]

Thanks! Will do first thing in the morning. I'll post the results.

 

[subzali]

BTW, you want another wire going to your carb to activate the idle circuit solenoid. The solenoid is located near the top of the carb, on the rear passenger's side.

 

[MarillaMarauder]

I know it's been awhile since this thread started but I recently purchased a '77 FJ40 and it is having this exact problem. However my idle goes to like 3000 RPM. Under all the same conditions that *maspers describes, the idle kicks down to normal idle (650 rpm) when I hit 10 mph. As soon as I accelerate and hit 10 mph this 3000 rpm mode kicks in until I go below 10 mph. I never touched anything on the carb before this problem started which leads me to think that it has nothing to do with any screw settings on the carb. One day it idled fine, the next this whacky high idle. I'd like to thank everyone in advance for their help and knowledge with these awesome vehicles. I have only owned my FJ for a few weeks but I find this site to be the first one to go to when I am looking for info. Tom

 

[Pin_Head]

Here is the throttle positioner speed adjuster and the linkage associated with the TP. If the speed adjuster is properly adjusted to give 1000 RPM above 10 MPH, maybe the linkage that actuates it is screwed up. It is vacuum operated under the control of the engine computer, so if the computer isn't working or the vacuum can leaks, it will be stuck on and will not pull off below 10 MPH.