Sticky throttle on a 1FZ-F (carburated)

[t00manyuserz]

Hi all, looking for some help, though realising that probably not many have a carbed engine here.

I have a somewhat sticky throttle. Basically, if I accelerate at WOT, it will definitely stick and rev high when clutched in, but even in normal driving, it’s a “little” sticky in that I have to pull back on it a little bit to reduce rpms. I’ve tried the following:

- replaced the throttle cable
- replaced the accelerator pedal assembly
- disconnected the hand throttle (in case it was pulling)
- even tried running with no throttle cable (see if the carb throttle sticks - but no, it’s perfect - also the carb is brand new)

It basically kinda feels like the pull back on the cable isn’t as strong as it should be. What could be the reason for this? Is it possible that some vacuum thingie is at fault? I’ve replaced the carb but I didn’t replace the round vacuum thingies.

Possible they’re bad and don’t pull the throttle back hard enough? Or am I knocking on the wrong door here?

 

[Cruising1South]

Hello,
I have a 1FZ-F 80 series. I have a similar issue…
I am in South America
Mine revs high when it’s hot, I can tap the accelerator pedal and it comes back down below 1000rpm. Sometimes it Revs back down fine and sometimes it stays up around 2K rpm. Happens more when the he motor is hot.

I have a new accelerator cable but haven’t put it on yet.

Also have a startup issue I’m trying to figure out. On a cold start it cranks right up. After driving or with a hot engine though it has trouble starting. It cranks and cranks and I have to mash the gas pedal to the floor or pump it and finally it starts up. I have replaced the starter so now it cranks stronger but still struggles to turn over without pumping the pedal.

I’m guessing vacuum issue? I have no idea where to start though

 

[t00manyuserz]

Hello,
I have a 1FZ-F 80 series. I have a similar issue…
I am in South America
Mine revs high when it’s hot, I can tap the accelerator pedal and it comes back down below 1000rpm. Sometimes it Revs back down fine and sometimes it stays up around 2K rpm. Happens more when the he motor is hot.

I have a new accelerator cable but haven’t put it on yet.

Also have a startup issue I’m trying to figure out. On a cold start it cranks right up. After driving or with a hot engine though it has trouble starting. It cranks and cranks and I have to mash the gas pedal to the floor or pump it and finally it starts up. I have replaced the starter so now it cranks stronger but still struggles to turn over without pumping the pedal.

I’m guessing vacuum issue? I have no idea where to start though

Some interesting points there.

1. The "stuck at high revs, tap accelerator pedal, goes to normal" thing I have as well. It's not as consistent as you describe, but it's the same thing - it will sometimes be idling higher than I like (maybe 1,200-1,500), I'll very gently tap the pedal and it'll drop right back to 800'ish. Can't figure out why.
2. The cranking is harder to say. Someone once told me that starting up a carb'd 1FZ is basically fuel, spark and ... I forgot one more thing, lol. But if you have crank (ah, maybe crank!) but no start, then maybe not enough fuel being served? Here is what happens with mine - that I consider "normal" at this point, part of life with a carb:
- I start the car, it starts up like a champ from cold.
- if I let it idle without touching the accelerator, it'll work for a bit and then not do the below.
- if I try to press the accelerator (i.e. to start driving), it will rev up, get fuel starved, and either stall (if I didn't floor the accelerator enough) or rev relatively high (>2K) and it almost looks like whatever vacuum voodoo it uses to pull fuel through JUST works in this case to pull enough fuel through, so it kind of hiccups, and then returns to a normal idle. --> so once again, to repeat: if I start and do not touch the accelerator, it will idle for 5 minutes and not have an issue, but if I press the gas soon after crank, it will immediately choke and either stall or, if I gave enough gas, just plow through what looks like fuel starvation. (Maybe vacuum insufficiency of some sort?)
- now, if I stalled it with the above footwork, then here's what I do. I leave the ignition on, and do not crank. I let it sit for about 10-15 seconds with all dashboard lights on - it looks like there's some vacuum in play because some fuel will get sucked into the engine. I might pump the gas pedal once, or I might not, but even if I do not, and wait 10-15 seconds, it will start right back up.

Also - yeah, now that I think about it, I do think it will also crank a bit on a hot engine. But again, if I let the ignition on sit there for a bit, it'll start right up. Try that?

I don't know if it's a vacuum issue or "that's just how carbs work". I'd be curious to hear other opinions but I feel like there aren't many people with one.

 

[Cruising1South]

I don't know if it's a vacuum issue or "that's just how carbs work"

When I purchased mine I looked at a few different 80 series and the owners all said the same thing. “Push the pedal to the floor to start it” was the advice they gave lol. I think a good mechanic could say otherwise. It definitely feels like a fuel delivery issue. And mine has a mechanical fuel pump, not sure if that is standard or likely a South American option.

I going to replace the accelerator cable soon and see if that helps. I live in an area with very dirty dusty roads so sticky cable seems posible. I have replaced the fuel filter and cleaned the carb with a spray cleaner since I’ve owned it(about 1 year)

I had a 95 Chevy and 93 Ford both with Carb that never needed any gas on startup….

 

[Cruising1South]

When I purchased mine I looked at a few different 80 series and the owners all said the same thing. “Push the pedal to the floor to start it” was the advice they gave lol. I think a good mechanic could say otherwise. It definitely feels like a fuel delivery issue. And mine has a mechanical fuel pump, not sure if that is standard or likely a South American option.

I going to replace the accelerator cable soon and see if that helps. I live in an area with very dirty dusty roads so sticky cable seems posible. I have replaced the fuel filter and cleaned the carb with a spray cleaner since I’ve owned it(about 1 year)

I had a 95 Chevy and 93 Ford both with Carb that never needed any gas on startup….

 

[t00manyuserz]

I wonder if mine has a mechanical fuel pump as well. I’m pretty certain it does. How did you tell, or just by the part number?

I’m actually not sure the throttle cable will help - unless the sheathing has failed at the carb end, I wouldn’t expect dust to be a major factor, but hey, you got one, so keep it. Did you get yourself a new carb btw? You might not need one but I ffgure if anything goes out of production in the next few years, carbs will - so you might want to buy one and put it on the shelf for the eventual eventuality of needing a replacement.

 

[Bardiya]

OEM Carb and OEM Throttle cable? I had a sticky throttle when running an aftermarket carb or throttle cable that was adjusted too tight.

All 1FZ-F have mechanical fuel pumps.

 

[Bardiya]

Some interesting points there.

1. The "stuck at high revs, tap accelerator pedal, goes to normal" thing I have as well. It's not as consistent as you describe, but it's the same thing - it will sometimes be idling higher than I like (maybe 1,200-1,500), I'll very gently tap the pedal and it'll drop right back to 800'ish. Can't figure out why.
2. The cranking is harder to say. Someone once told me that starting up a carb'd 1FZ is basically fuel, spark and ... I forgot one more thing, lol. But if you have crank (ah, maybe crank!) but no start, then maybe not enough fuel being served? Here is what happens with mine - that I consider "normal" at this point, part of life with a carb:
- I start the car, it starts up like a champ from cold.
- if I let it idle without touching the accelerator, it'll work for a bit and then not do the below.
- if I try to press the accelerator (i.e. to start driving), it will rev up, get fuel starved, and either stall (if I didn't floor the accelerator enough) or rev relatively high (>2K) and it almost looks like whatever vacuum voodoo it uses to pull fuel through JUST works in this case to pull enough fuel through, so it kind of hiccups, and then returns to a normal idle. --> so once again, to repeat: if I start and do not touch the accelerator, it will idle for 5 minutes and not have an issue, but if I press the gas soon after crank, it will immediately choke and either stall or, if I gave enough gas, just plow through what looks like fuel starvation. (Maybe vacuum insufficiency of some sort?)
- now, if I stalled it with the above footwork, then here's what I do. I leave the ignition on, and do not crank. I let it sit for about 10-15 seconds with all dashboard lights on - it looks like there's some vacuum in play because some fuel will get sucked into the engine. I might pump the gas pedal once, or I might not, but even if I do not, and wait 10-15 seconds, it will start right back up.

Also - yeah, now that I think about it, I do think it will also crank a bit on a hot engine. But again, if I let the ignition on sit there for a bit, it'll start right up. Try that?

I don't know if it's a vacuum issue or "that's just how carbs work". I'd be curious to hear other opinions but I feel like there aren't many people with one.

Some of what you are describing is normal when cold. There is a fast idle cam that will shoot up the revs when cold and will disengage once you push on the throttle.

The 1FZ-F has multiple systems in place to improve cold start and drivability but they all need to be working and adjusted properly otherwise they are more trouble than they are worth.

Systems such as:

Electronic Choke
Outer Vent Control Valve
Fast Idle Cam
Auxilary Accelerator Pump
VSV for ignition advance and VSV for A/C idle up

Most of these systems can be deleted or bypassed for simplicity. You can find detailed explanations on the 1FZ service manual under "Fuel System"

 

[t00manyuserz]

Some of what you are describing is normal when cold. There is a fast idle cam that will shoot up the revs when cold and will disengage once you push on the throttle.

The 1FZ-F has multiple systems in place to improve cold start and drivability but they all need to be working and adjusted properly otherwise they are more trouble than they are worth.

Systems such as:

Electronic Choke
Outer Vent Control Valve
Fast Idle Cam
Auxilary Accelerator Pump
VSV for ignition advance and VSV for A/C idle up

Most of these systems can be deleted or bypassed for simplicity. You can find detailed explanations on the 1FZ service manual under "Fuel System"

Very interesting - thanks! I don't have any desire to bypass anyting for now while everything works perfectly, but that WOULD explain the initially high idle and so on.

One note on the throttle cable: I did have a ridiculous stickiness while cable was overly tight. I initially followed the FSM and tightened it while idle and then loosened it to a couple of cm of slack, but that was way too tight. I have now adjusted it so it's almost completely loose, just almost at the point where the accelerator pedal flaps about (but not quite), and now my throttle works well. So if you're experiencing a sticky throttle, do check if your cable is overtightened.

 

[Bardiya]

Very interesting - thanks! I don't have any desire to bypass anyting for now while everything works perfectly, but that WOULD explain the initially high idle and so on.

One note on the throttle cable: I did have a ridiculous stickiness while cable was overly tight. I initially followed the FSM and tightened it while idle and then loosened it to a couple of cm of slack, but that was way too tight. I have now adjusted it so it's almost completely loose, just almost at the point where the accelerator pedal flaps about (but not quite), and now my throttle works well. So if you're experiencing a sticky throttle, do check if your cable is overtightened.

I had the exact same issue when replacing my throttle cable. Fully loose it works fine now.