Cruise Control Locking Up

[mgroeger]

2004 LJ 111k miles.
I turn the cruise control on and the light comes on. I then engage cruise control and the gas pedal locks into place (I'm assuming this is supposed to happen) but the throttle does not lock into place. The engine simply idles and I gradually slow down because I'm not actually in CC mode.
I have to cancel or turn CC off to regain pedal ability.

 

[mgroeger]

I just saw this...
"Check to make sure your head system blows out of the appropriate vents you select. If it always blows out of defrost then it is probably a vacuum leak causing the cruise problem"
I did notice that when I have the vent selection on face that it comes out the floor and face about the same. I don't believe it should be blowing that hard out the feet when it is on face. A little can be expected but not as much as I'm seeing.

 

[Chris]

The likely explanation is that you have a vacuum leak somewhere, as cruise control runs of vacuum, as does the vent selector.

 

[mgroeger]

Thanks. Time for a hose check.

 

[mgroeger]

@Chris
Well I checked all of the hose connections. I noticed the main feed that comes off of the intake manifold (pretty much right there in front of the big round cruise control unit) was a little sloppy so I zip tied it tight. That seemed to help with the HVAC control damper, where you change from face, to feet, to defrost, etc... They now seem to be changing firmer with a definitive "click"and truly blowing out where they should be.
This did nothing to help the CC though. The CC still engages in that it locks the pedal in place but the engine goes to idle and does not maintain speed/RPMs. What is the next thing I can look at? Is there a way to crack that CC unit open to see if the vacuum is messed up in there? The CC unit is doing something in that it is locking the pedal at least.
I guess I also could disconnect the vacuum line from after the CC to make sure there is absolutely nothing effecting the CC.

 

[Chris]

@Chris
Well I checked all of the hose connections. I noticed the main feed that comes off of the intake manifold (pretty much right there in front of the big round cruise control unit) was a little sloppy so I zip tied it tight. That seemed to help with the HVAC control damper, where you change from face, to feet, to defrost, etc... They now seem to be changing firmer with a definitive "click"and truly blowing out where they should be.
This did nothing to help the CC though. The CC still engages in that it locks the pedal in place but the engine goes to idle and does not maintain speed/RPMs. What is the next thing I can look at? Is there a way to crack that CC unit open to see if the vacuum is messed up in there? The CC unit is doing something in that it is locking the pedal at least.
I guess I also could disconnect the vacuum line from after the CC to make sure there is absolutely nothing effecting the CC.

I think you may in that case have a bad cruise control servo. There's no way to open them up to my knowledge, I think it's one of those parts where once it breaks, you have no choice but to get a new one unfortunately.

That would be my best guess at least, being as though the cruise control setup is very simple. It's just the buttons, the servo, and a throttle cable. If it isn't the vacuum hoses, my bet is on the servo.

 

[mgroeger]

Thanks! Well at least it's simple

 

[mgroeger]

I think you may in that case have a bad cruise control servo. There's no way to open them up to my knowledge, I think it's one of those parts where once it breaks, you have no choice but to get a new one unfortunately.

That would be my best guess at least, being as though the cruise control setup is very simple. It's just the buttons, the servo, and a throttle cable. If it isn't the vacuum hoses, my bet is on the servo.

So ultimately it is "working" in that it is receiving the signal and locking the gas pedal, it just isn't locking the throttle cable. Wait... how does the cruise work on the wrangler. Does it actually lock the gas pedal in place like I am stating? I thought that kind of odd and dangerous since that means you can't give it gas in an emergency, the pedal is literally locked in place. You would have to coast or cancel cruise to make an adjustment. I'm wondering if when the guy had the intake and exhaust manifolds off that he put something in backwards, like swapped where the cables go.
He said prior to working on the manifold gasket it worked perfectly. I'm going to go see if I can find pics of what it is supposed to look like. Feel free to post your own

 

[Chris]

So ultimately it is "working" in that it is receiving the signal and locking the gas pedal, it just isn't locking the throttle cable. Wait... how does the cruise work on the wrangler. Does it actually lock the gas pedal in place like I am stating? I thought that kind of odd and dangerous since that means you can't give it gas in an emergency, the pedal is literally locked in place. You would have to coast or cancel cruise to make an adjustment. I'm wondering if when the guy had the intake and exhaust manifolds off that he put something in backwards, like swapped where the cables go.
He said prior to working on the manifold gasket it worked perfectly. I'm going to go see if I can find pics of what it is supposed to look like. Feel free to post your own

I'm not entirely sure how it works to be honest. I'd have to look at the diagrams.

But I know it's powered by vacuum, and that vacuum is what holds down the pedal and pulls open the throttle using the cable coming from the cruise control servo.

There's not really much that can go bad. It's either vacuum leaks or the servo itself.

When the buttons are bad, then you can't even get the light to go on to begin with (happened to me once).

 

[mgroeger]

Wow, so it actually locks the pedal in position. I'm kind of shocked at that since you really are screwed if in an emergency you need to jump on the gas to accelerate.

 

[Chris]

Wow, so it actually locks the pedal in position. I'm kind of shocked at that since you really are screwed if in an emergency you need to jump on the gas to accelerate.

All you have to do is apply the brake (even very softly) and it disengages the cruise control, so the pedal is no longer locked in position. It's not actually "locked", it's just at the point of travel that it takes to get to maintain the speed.

Nothing dangerous about it at all.

 

[NavyHorn]

2004 LJ 111k miles.
I turn the cruise control on and the light comes on. I then engage cruise control and the gas pedal locks into place (I'm assuming this is supposed to happen) but the throttle does not lock into place. The engine simply idles and I gradually slow down because I'm not actually in CC mode.
I have to cancel or turn CC off to regain pedal ability.

Did you ever figure out what was causing this? Mine has been the same for years. I just swapped the servo with a salvaged part, but no joy.

 

[SkylinesSuck]

I think I did something similar to this once. I have a manual transmission. I had disconnected the cables to the TB and installed them back incorrectly. I put the cruise cable on what was meant for the auto tranny kick down cable.

 

[MRChiefE7]

Check the cable connection at the TB. I had mine come off one time.

 

[dyermullet]

I think I did something similar to this once. I have a manual transmission. I had disconnected the cables to the TB and installed them back incorrectly. I put the cruise cable on what was meant for the auto tranny kick down cable.

2004 LJ 111k miles.
I turn the cruise control on and the light comes on. I then engage cruise control and the gas pedal locks into place (I'm assuming this is supposed to happen) but the throttle does not lock into place. The engine simply idles and I gradually slow down because I'm not actually in CC mode.
I have to cancel or turn CC off to regain pedal ability.

I just wanted to post a reply in case someone else finds this through a search. TJ was doing same thing as OP. Turn on cruise control vehicle slowed down and pedal hard as a rock. Previous owner had installed the cruise control onto the transmission cable lever. Anytime the cruise was turned on it pulled the throttle closed. Very dangerous problem, not having an operable throttle.

 

[Moglocker]

All you have to do is apply the brake (even very softly) and it disengages the cruise control, so the pedal is no longer locked in position. It's not actually "locked", it's just at the point of travel that it takes to get to maintain the speed.

Nothing dangerous about it at all.

And you can also increase the speed one mile an hour with every push of the accel button.

 

[jjvw]

Going back to the very start of this, can someone explain how the cruise control system locks the gas pedal? (Because it doesn't and it can't)

 

[jjvw]

I just wanted to post a reply in case someone else finds this through a search. TJ was doing same thing as OP. Turn on cruise control vehicle slowed down and pedal hard as a rock. Previous owner had installed the cruise control onto the transmission cable lever. Anytime the cruise was turned on it pulled the throttle closed. Very dangerous problem, not having an operable throttle.

How exactly does one connect the cruise control to the transmission cable lever?

 

[dyermullet]

Not sure if this is a troll post or serious. But since it was such a dangerous situation and easy to correct I will respond in case someone else finds this in search like I did.

Their are three connection points on the throttle body one is for throttle cable, one is for cruise cable, one is for a transmission cable. The throttle cable and cruise cable pull is same direction on the throttle shaft, the transmission cable is on opposing side of the throttle shaft. In my case the previous owner connected the cruise cable to the transmission point on the throttle body. Turn on the cruise and press SET the cruise control will pull the throttle closed instead of pulling it open. This will bring the engine to idle and you cannot over come that with your foot. Have to cancel the cruise control to get operation of the gas pedal back.

Make sense?

I was able to clip the cruise cable onto the correct point and now have restored functional cruise.

 

[SkylinesSuck]

That is how it works, yes.