24in of vacuum at idle too high for the 2.8L?

[8thTon]

The hot idle compensator isn't in the air cleaner, it would mount to the back of the carb. The piece in the air filter shouldn't be capped. Vacuum should feed one side of the vacuum valve and the other side would connect to the air cleaner vacuum motor that allows warm air to be drawn into the air cleaner during warm up.

Yes, you’re correct and I’m getting rusty on those parts. It’s the air filter thermostat.

 

[SgtDan94]

Your throttle plates should not be closing so far that they bind in the throttle bores, they are supposed to hit a mechanical stop (idle speed adjust). If your idle is too high then you likely have a vacuum leak somewhere. If it's small you may be able to tune it in terms of mixture, but it will still add air and increase idle.

Sometimes a hot idle device is added, which is a small bimetal thermostatically activated air leak intended to increase idle speed on hot engines. This could be mounted in the air filter housing. It looks like what I'm seeing in your picture, but it's hard to tell. If that has failed open then it would be your high idle problem. Plug it and see what happens, it's no big deal to run without it for a while. If you plug it disconnect the hose and plug it at the line, covering that exposed tube won't work.

A larger tube may run into the air filter which could be the fuel bowl vent. That would not have anything on it.

@SgtDan94 ...

Something else I noticed in your picture... The air cleaner snorkel is missing the flexible coupler between the air cleaner and the cold air intake. This would allow heated air in the engine compartment to be drawn into the air cleaner opposed to drawing in fresh air from the front of the vehicle. You should look into sourcing one of those...

it does seem a bit odd to me that it idles ok with the adjustment backed all the way out..

Im going to replace all the old plastic vacuum lines with some rubber vacuum hose. I did this on a 1990 F-150 with a 5.0 and it solved a lot of problems. I noticed a lot of the rubber vacuum 90s on the Bronco are cracked up or stretched out. The good news is that the vacuum system on the Bronco II is a lot more simple than the F150, or at least more accessible. I’m going to do that today and I’ll update the thread.

Thanks again

 

[85_Ranger4x4]

@SgtDan94 ...

Something else I noticed in your picture... The air cleaner snorkel is missing the flexible coupler between the air cleaner and the cold air intake. This would allow heated air in the engine compartment to be drawn into the air cleaner opposed to drawing in fresh air from the front of the vehicle. You should look into sourcing one of those...

That made a big difference on my 2.8.

Mine was falling apart so I trashed it. Then the truck ran horrible... so I fished it out of the trash and duct taped it back together... and all was well.

 

[SgtDan94]

@8thTon @Uncle Gump @85_Ranger4x4

Replaced all vacuum lines with good new rubber (see attached) and reset the mixture screws on the carb using the vacuum gauge. Also replaced the PCV lines. Bronco runs noticeably smoother... the engine shakes a lot less While it’s idling and I’m still getting 24-25 in of vacuum according to the gauge. Can you guys listen to it and let me know what you think? It sounds like a diesel to me.. Here’s a link to the video:

BRONCO II 2.8 idle

I’ll go ahead and install the air snorkel tube once I track one down... but what about the hot air intake tube that’s coming up from the exhaust manifold? I live in central California where it never gets colder than 45 degrees.. do I need this tube installed or can I cap off the inlet to the intake?

thanks

 

[Uncle Gump]

I don't think it sounds to bad... it has the tick that is pretty normal for those things. It appears to run really smooth.

You probably don't need any of the heated air system... being you live where you live. The tube from the exhaust manifold to the snorkel is probably not needed.

You should probably check the operation of the flapper in the snorkel though. When cold... it should close off the cold air intake and draw heated air from the exhaust. When warm... it should open so the cold air comes in from the cold air inlet and closes off the heated air side.

 

[SgtDan94]

I don't think it sounds to bad... it has the tick that is pretty normal for those things. It appears to run really smooth.

You probably don't need any of the heated air system... being you live where you live. The tube from the exhaust manifold to the snorkel is probably not needed.

You should probably check the operation of the flapper in the snorkel though. When cold... it should close off the cold air intake and draw heated air from the exhaust. When warm... it should open so the cold air comes in from the cold air inlet and closes off the heated air side.

Thanks for the help. I’m gonna go to a junk yard to find the the rest of the intake and then take it in for a SMOG.

Does anyone know if you can pull trouble codes from the 1984? It has the OBD1 triangular port under the hood, however I don’t think it has a check engine light so I can’t jump the test port to pull codes.

 

[8thTon]

Sounds good to me - are the throttle plates set on the idle adjust stop or are they fully closed?

 

[SgtDan94]

Sounds good to me - are the throttle plates set on the idle adjust stop or are they fully closed?

They are fully closed, not resting on the idle adjust. It seems to run fine, I’ll find out for sure once there’s a tachometer installed

 

[SgtDan94]

I can’t seem to find that missing ram air intake hose.. the middle piece that’s missing.. I guess I’ll be making one

 

[8thTon]

They are fully closed, not resting on the idle adjust. It seems to run fine, I’ll find out for sure once there’s a tachometer installed

Well then there is air going around them and into the intake somewhere - it may work ok but it isn't quite right.

 

[SgtDan94]

Well then there is air going around them and into the intake somewhere - it may work ok but it isn't quite right.

@Uncle Gump

What about the mixture control solenoid on the back of the carb.. can this cause high idle? Maybe I should unplug it and see if it make a difference while running... I know for a fact that my coolant temperature sensor is no good, however I don’t know if changing it out is going to affect the idle on this engine like it would on a EFI engine

and by high idle, I mean “normal” idle but with the screw all the way out...

I supposed it’s possible that someone else took the two plates off the shaft and didn’t put them back on correctly...

 

[19Walt93]

If it's idling with the adjustment screw backed out there's something wrong. I've never seen an engine with 24" of vacuum, how did you measure it?

 

[SgtDan94]

If it's idling with the adjustment screw backed out there's something wrong. I've never seen an engine with 24" of vacuum, how did you measure it?

I T'd my vacuum gauge off of the vacuum line running from manifold vacuum tree to the large sensor, i assume the MAP sensor, located over by the vacuum solenoids. It is possible that my vacuum gauge is off, its brand new and i know that out of the box it was reading 1in of vacuum probably just from atmospheric pressure.

Today im going to replace the coolant temp sensor and air temp sensor in the intake. Again, i dont know if these sensors effect the idle like they do on a EFI engine, but i do know that they are bad and need replacing. Coolant gauge moves but doesnt read past the "C" at the bottom pf the gauge even after idling/ driving 20 minutes.

This Bronco sat in a barn since 1997, so its got some kinks. However it appears it was very well taken care of back in the day, 150,000 on the odometer.

 

[SgtDan94]

@19Walt93

I still need to find out if a bad air/ mixture control solenoid on the back of the carb would cause bad/ high idle. I dont know for sure if mine is burned out however it looks super old oxidized. I assume this is the same as an idle air control valve on a EFI engine.


I believe that i have high idle that i compensate for by backing out the idle screw all the way.

 

[8thTon]

@19Walt93

I still need to find out if a bad air/ mixture control solenoid on the back of the carb would cause bad/ high idle. I dont know for sure if mine is burned out however it looks super old oxidized. I assume this is the same as an idle air control valve on a EFI engine.


I believe that i have high idle that i compensate for by backing out the idle screw all the way.

Can you post some pictures of the carb from the sides or back?

The mixture control solenoid is just that, it is not the same as the Idle Air Control Valve which does not effect mixture, only controls idle speed by allowing air to flow around the throttle plate.

It is almost guaranteed that there is an air/vacuum leak feeding air into the intake and bypassing the carb. This could be almost any device on the vacuum diagram, you really have to check them one by one. I used to have a scanned document of all the vacuum devices used on Fords, and will try to find it.