Throttle icing up..? (1 Viewer)

[Vision19]

Good morning everyone,
Temps are getting cold here in AK. This morning was -30 F. I had the cruiser's (94) block heater plugged in all night. I let it warm up for 10 mins before I started the drive to work. After 5 minutes of driving, my throttle became stuck open at about 3000 rpms. It would not come down even after pumping the throttle pedal quickly. I made it the last mile or so to work and shifted to park, got out and physically worked the throttle body lever to unstick it.

My throttle cable is less than 2 years old and is still smooth. I had my intake boot off last weekend and cleaned up any residue I found in the throttle body area. Has anyone ever encountered throttle body icing before? I know it is very common in aviation - carb icing - but that is on carburetors only. Maybe I need to take apart the throttle body to clean the mechanisms out really well?

Thoughts and opinions appreciated.

 

[Kernal]

Shaft for the butterfly valve got stuck ??. Possibly due to ice and/or tolerances changing from the extreme cold?? Nothing works very well at those temps.

Are your bypass hoses for Throttle Body heat connected?

 

[Vision19]

Yes i believe it was the shaft for the butterfly that was stuck. I don't think the bypass hoses have been messed with at all but I will check on that.

 

[rdcnj]

Yes i believe it was the shaft for the butterfly that was stuck. I don't think the bypass hoses have been messed with at all but I will check on that.

Had that happen recently and it was causing the same exact issue. I used spray silicone to completely clean the butterfly of any debris (dust, dirt, etc).

Worked well.

 

[Vision19]

I pulled the intake boot off and I found considerable water inside the throttle body. I also disconnected the hose on the valve cover next to the PCV that goes into the throttle body and it is filled with oil/water vapor milk shake. I don't think that hose should be pushing air from the valve cover into the throttle body correct? The water vapor explains the icing up, but now I need to figure out why so much vapor. I do have a catch can on my PCV line. Maybe that is so crudded up that I'm pulled vacuum on the other side?

 

[ZackR]

How far is your drive to work? Looks like the oil never warms up enough to evaporate the moisture.

 

[jpoole]

Have you kept your catch-can emptied?

The catch can on my 80 picks up a lot of moisture in the cold and will fill up if I follow the normal empty interval that I follow in warmer months. Perhaps your catch can filled up and you then sucked the water into the manifold via the PCV line and the cold intake air froze it in the throttle body?

 

[Vision19]

My drive is only about 6 miles at 45 mph max. I emptied my catch can last weekend. But I would agree I doesn't seem to be evaporating moisture away

 

[Mark W]

It takes a lot of moisture in the air to get carb icing. It also takes warmerer air so that the moisture can be in suspension. It is the dropping of the temps as they pass through the intake tract and cool due to expansion which causes carb icing. To the best of my knowledge it can nor happen with the ambient temps that we are having here currently.

FWIW, without sitting and digging in the back of my brain, I am not remembering any reason that "carb" icing can not happen in a fuel injected engine as well.

That said, it might be possible to reach the temps and moisture levels within that gunked up hose (being warmed by the engine itself) so that that very small portion of the system is within the zone. But I question if there would be enough water able to evaporate into the (small amount) of air passing through those hoses to get enough vapor into the intake air to then get enough precipitating out again immediately to create enough ice on the throttle shaft to make it bind.

I have encountered carb icing a couple of times over the years. In ATVs operated in powder snow at very sub zero temps and in carbed automotive engines (2Fs actually) operated in similar conditions. But those instances had a LOT of powder being thrown up all over everything into the engine bay in the case of the cruiser). The rigs were crusted with melted and refrozen snow. I have never seen it happen or heard of it happening on a road rig with the temp/wx conditions like we have at the moment.

I am thinking that it is more likely changing clearances due to the extreme cold creating a mechanical bind. Or maybe oily deposits in the throttle assembly ( or actual lube in the cable) stiffening up.


Mark...

 

[Kernal]

So are you going to disconnect the catch can for now (put the hoses back to stock configuration)??

How does the engine oil look?
Thermostat operating normally (engine reaching operating Temps)??

 

[LongDuck]

Speaking from the aviation end, carb icing results in noticeable power loss, not a frozen linkage or stuck throttle. The venturies within the carb are what ice up given the sudden drop in air pressure, which then prevents fuel flow into the venturi. Any loss of power at altitude results in pulling the carb heat lever, which opens up warm exhaust manifold air to the intake. Once the ice is melted, carb heat off, and the power comes back.

As the other guys said, your Throttle plate likely froze to the throttle body, and that's due to the excess moisture in the intake path, possibly water or oil / grease on the linkages and where the throttle rods go through the throttle body.

 

[Mark W]

Speaking from the aviation end, carb icing results in noticeable power loss, not a frozen linkage or stuck throttle. The venturies within the carb are what ice up given the sudden drop in air pressure, which then prevents fuel flow into the venturi. Any loss of power at altitude results in pulling the carb heat lever, which opens up warm exhaust manifold air to the intake. Once the ice is melted, carb heat off, and the power comes back.

As the other guys said, your Throttle plate likely froze to the throttle body, and that's due to the excess moisture in the intake path, possibly water or oil / grease on the linkages and where the throttle rods go through the throttle body.

^^ Very true. I should have pointed that out too. Loss of power would be the first thing that would be noticed. By the time any ice formed from "carb icing" would be making the throttle stick, you'd liking be stumbling and just barely running.

Mark...

 

[Vision19]

My suspicion at this point is a few factors combined: lots of "warm up" idling that causes condensation and possibly too much gunk in the passage ways of the catch can. Once I open the throttle up while driving it sucks in all the excess moisture and voila, frozen butterfly valve. I have removed the catch can for now and put hoses back to stock configuration. I cleaned out the hoses and throttle body and lubed the butterfly valve with some Tri-Flo. I am going to do a much shorter warm up idle for the next few days and see what the resuts are. The block heater does a pretty good job of inital heating anyway. Thanks for all the input.