Idle racing and hard/frozen brake pedal

[ccslider]

For the racing idle I would suspect a vacuum leak at the engine. Its sucking in air somewhere. I would first check the throttle body operation. With the engine off and the air intake hose removed, have someone press the throttle pedal in the truck while you watch. Use your phone and record it if you are alone. If that checks out good with consistent movement then I would do the carb spray test. Spray the vacuum hoses and connections,when the engine races more you know its sucking in the fuel "carb spray" at the leak.

If you have a vacuum leak at the engine then you will not be able to achieve vacuum for the brake booster diaphragm and have a hard pedal.

I included the link for the fsm manual. Select the 80's chassis then goto the brake section BR16 and you will find the information you seek. Check out BR7 too for the brake booster test.


good luck

 

[TomOsborne]

For the racing idle I would suspect a vacuum leak at the engine. Its sucking in air somewhere. I would first check the throttle body operation. With the engine off and the air intake hose removed, have someone press the throttle pedal in the truck while you watch. Use your phone and record it if you are alone. If that checks out good with consistent movement then I would do the carb spray test. Spray the vacuum hoses and connections,when the engine races more you know its sucking in the fuel "carb spray" at the leak.

If you have a vacuum leak at the engine then you will not be able to achieve vacuum for the brake booster diaphragm and have a hard pedal.

I included the link for the fsm manual. Select the 80's chassis then goto the brake section BR16 and you will find the information you seek. Check out BR7 too for the brake booster test.


good luck

Thank you. Im going to keep on it until I figure it out myself. Thinking that the booster could seize like that with some vacuum has been hard to digest but the high idle coinciding is hard to ignore. The idle isn't racing like it was after spraying the cables but it is still higher than it was before the brake pedal. Many thanks for everything you offered!

 

[Tools R Us]

Depending on year, model, it can code for a big vacuum leak, any codes? Slippery stuff improved the idle, guessing the cable is shot, can the linkage manually be returned to idle, try it with the cable disconnected? Most often when a booster fails it has good vacuum, the valve dies. FSM: For Sale - 40, 50, 60, and 80 series FSM for a hell of a price.

 

[bob82pigdog]

I too am trying to track down a similar issue. Is your brake pedal always hard or only when the high idle is happening? Reason I'm asking is because I had something similar happen with my brakes but only once, when the idle got out of control. I think fix the high idle, then the brakes may not be an issue anymore.

Sitting in bumper to bumper traffic the other day, I felt the truck idling high, popped it into neutral and RPMs shot to 1200. Kept driving, it's happened before. Popped in neutral again a few minutes later, 1600 RPM. Kept driving until, eventually I couldn't stop the truck with the brakes, it wanted to take off it was idling so high, popped it into neutral and RPMs shot up to 3000. At the same time my coolant gauge was getting hot so I had to pull over and let the engine cool down.

When I got home I hosed off the radiator really well just in case some mud or something was clogging up the fins. It still idles high sometimes but it's not preventing me from driving anywhere. I haven't had the brakes lose the fight against the motor again, at least.

So far these two threads below seem to have some useful troubleshooting info, but I haven't had much time to try anything yet. Is it a bad coolant temp sensor? Idle Air Control Valve? Throttle Position Sensor? Vacuum leaks? With 278k miles, who knows it could be all of those on my truck!

FJ80 High Idle Problem Solved

New High Idle when Warm Problem

 

[TomOsborne]

I too am trying to track down a similar issue. Is your brake pedal always hard or only when the high idle is happening? Reason I'm asking is because I had something similar happen with my brakes but only once, when the idle got out of control. I think fix the high idle, then the brakes may not be an issue anymore.

Sitting in bumper to bumper traffic the other day, I felt the truck idling high, popped it into neutral and RPMs shot to 1200. Kept driving, it's happened before. Popped in neutral again a few minutes later, 1600 RPM. Kept driving until, eventually I couldn't stop the truck with the brakes, it wanted to take off it was idling so high, popped it into neutral and RPMs shot up to 3000. At the same time my coolant gauge was getting hot so I had to pull over and let the engine cool down.

When I got home I hosed off the radiator really well just in case some mud or something was clogging up the fins. It still idles high sometimes but it's not preventing me from driving anywhere. I haven't had the brakes lose the fight against the motor again, at least.

So far these two threads below seem to have some useful troubleshooting info, but I haven't had much time to try anything yet. Is it a bad coolant temp sensor? Idle Air Control Valve? Throttle Position Sensor? Vacuum leaks? With 278k miles, who knows it could be all of those on my truck!

FJ80 High Idle Problem Solved

New High Idle when Warm Problem

Nice getting more input- thank you. Ive been slowly chipping away at it. I will have a bit of time this evening so I might even get to the point where I'll start it.

Is your brake pedal always hard or only when the high idle is happening?
My idle started increasing in s similar manner you described. I left for home and when I tried to use the brakes they were rock. Been in that state since.

At the same time my coolant gauge was getting hot so I had to pull over and let the engine cool down.
My temp stayed in check. Small victories.

It still idles high sometimes but it's not preventing me from driving anywhere
Currently mine are about 1200 at idle. But if it is vacuum related we should see them coming down shortly.

Is it a bad coolant temp sensor? Idle Air Control Valve? Throttle Position Sensor? Vacuum leaks?
SmokingRocks -lol, has been very gracious and has helped me with attacking this. The most logical place to look is at the vacuum. Over the weekend I realized that just about half of my vacuum lines were shot. If the hose carries air there is something I can do to improve it. So I'm not even concerned at the moment about doing anything else but fixing that mess. Next step will be to pull codes I'd imagine.

Thanks again friend. I'll see about posting back as soon as I can.

 

[ChaseTruck]

Perhaps check this out:
1993 Fj80 Rough Idle, runs great other than that

 

[TomOsborne]

Perhaps check this out:
1993 Fj80 Rough Idle, runs great other than that

Man this is great stuff. Thanks for the heads up!

 

[TomOsborne]

Had more time to work on it this weekend. Just replaced the vacuum lines really. Found several cracks here and there. Still have the hard pedal but it did seem to change just a little. I have enough play in the pedal where I can here a constant hiss when it is depressed. Dont remember that happening before, and the idle drops a hundred or so rpm's too - while depressed. Time to pull some codes....

 

[TomOsborne]

Well that was fun lol. As far as I can tell I have one constantly blinking code. Rewired the jumper, same result. Input? Thanks yall - Happy Sunday. May your truck run well today.

 

[TomOsborne]

From what I could tell the constant blink I mentioned above was for "all clear", which is nice to figure out. To date I have removed the air can, all vacuum hoses to and from said air can, replaced almost every one, fixed a gigantic hole on the intake tube that was the inlet for the smog pump, pulled the throttle body, cleaned the hell out of it, fixed a gigantic kink from the inlet pipe coming from the snorkel; as the pipe entered the engine the 45 or so degree bend to the air can was at least 60% restricted, and waiting on the throttle body gasket. For what its worth, here's a look at the throttle body... Tonight its the PCV and a new grommet, and new cooling lines to the throttle body. I'll note that there was a crapload of crap in the intake line to the TB so when I pulled the throttle body, there was lots of rusty water that pooled out. So Im close to seeing if this a)brings down my idle, and b)does anything to the frozen brake pedal. May your LC run like a scalded puppy today.

 

[TomOsborne]

Maybe someone will get something out of this someday. Currently I've just got a headache. Everything is back together. New PCV grommet and didn't lose any down the VC. Rare win. New hoses and clamps. Clean TBD and new gasket. Still wondering why that gasket appeared so "generic". Put it on as is. TPS looked brand new. I guessed it would be thoroughly gummed. Guessing it is fairly new. Did not pull the IACV. It was getting late and I may have a missing vac line coming off the air can- need to look it all over with a fresh set of eyes. Not sure exactly where the distributor vacuum lines go. I think the big one might go to the firewall by the CC? Little one I have no idea at t he moment. Couldn't help buto want to crank it. Severe bounce idle and a couple backfires so shut it down immediately. Plan is to add some coolant and try to bleed the cooling system, pull the EFI fuse, drink 2 beers and go from there. Also going to change oil to a high mileage 5w 30 sinice I'm still in full shutdown mode and seems like a good idea going forward. Hope yall are well thanks for reading and any advice is appreciated!

 

[TomOsborne]

Alright me again. Sorry in advance but Ill throw a line out there. After replacing almost every vacuum line, finding several cracks - big ones at that, and cleaning the throttle body, checking the TPS, etc I have my rig back together. When I start it, the idle bounces from 1900-2200 without fail, backfires, but most strange is the gas pedal is not even recognized. When the throttle is bouncing the rig doesnt even recognize I am pushing on it. She will will stay running, although its tough to hear it backfire, and it was burping air out of the radiator while doing so, but not recognizing the gas pedal? What in the world could be going on there? Any ideas? Thanks in advance and sorry for the bump.

 

[TomOsborne]

Thinking out loud here, what else can it be but the TPS. Not that I have ever messed with one but I sure as hell have now. So, I put it on at about 11:00, got tension against the TPS spring and slit it back to 12:00 (the top mounting screw/adjustment) and screwed it back on exactly where it was- dead center 12:00. And then there is the replacement throttle body gasket. Admittedly I do not know what the machined orifices do on the back side of the throttle body. The new gasket did not allow for these orifices and everything is covered by the gasket and I am fairly sure the old gasket had cut outs there. For now I plan on cutting a new gasket, retesting the TPS, and going from there. Feel free to solve my problem lol. Thanks again. Oh, and attempting to pull codes AND further bleeding the cooling lines as its still burping.

 

[bob82pigdog]

Thanks for updating with posts. Sorry, I still don't have much info. Buut, this weekend, new modded blue hub fan clutch, new water pump, new thermostat, and new silicone PHH are getting installed with a thorough flushing and replacement of coolant. Let's see if that does anything for me. Hopefully no more overheating, but we'll see if that high idle comes back.

 

[TomOsborne]

Thanks for updating with posts. Sorry, I still don't have much info. Buut, this weekend, new modded blue hub fan clutch, new water pump, new thermostat, and new silicone PHH are getting installed with a thorough flushing and replacement of coolant. Let's see if that does anything for me. Hopefully no more overheating, but we'll see if that high idle comes back.

This is turning more into a diary/journal for my vehicle. Thanks for hanging in there. After spending another evening and morning figuring out my next plan of attack and not just going off my initial disappointment of failing in my 30 minute window after work, I'm thinking this:

-I ended up pulling the plug on the TPS while it was idling just to see what would happen. Off to the races. Shut it down and plugged it back in.

-This may be the MAF. I had it off, cleaned it, and the car would react this way if it were contaminated, or while taking its part in the relearn process. I still am surprised that whatever my problem is it has completely hijacked my gas pedal for the time being. Never would have guessed that could even happen on any vehicle. So I'm thinking of unplugging it after I start it this evening just to see how the LC reacts.

-I know I still have air in my cooling lines so I'll jack it up and go full burp again while monkeying around with the MAF.

Thanks for reading.

 

[Lowbudgetlc100]

sound like a brake booster hose.

 

[TomOsborne]

sound like a brake booster hose.

That was the consensus, or a vac leak somewhere else. So I replaced just about every vacuum line and examined the rest, plus a thorough check and cleaning of everything from the intake manifold back. Now it's back together and it runs like hell with a bounce in the idle, and the ECM is overriding my gas pedal input, which again I think is just nuts. Still dont know if the brake pedal/booster benefited from the vacuum line fixes. Would like to drive it around the neighborhood to help with the relearn, but without the rig accepting my pedal thats a big fat no. So thats where I think the MAF is screwing with me.

 

[Tools R Us]

... When I start it, the idle bounces from 1900-2200 without fail, backfires, but most strange is the gas pedal is not even recognized. ...

Almost always TPS related. Not necessarily the switch, but idle signal not getting to the ECU, adjustment, bad connection, etc.

 

[TomOsborne]

Almost always TPS related. Not necessarily the switch, but idle signal not getting to the ECU, adjustment, bad connection, etc.

Thanks for your help! My LC will be great again.

 

[TomOsborne]

Almost always TPS related. Not necessarily the switch, but idle signal not getting to the ECU, adjustment, bad connection, etc.

Alright my man, Mr. Weekend crappy mechanic is back at it again, and this time I have some codes! #24 & #41. So I'm happy, and it's exactly where you pointed me (intake air temperature and TPS codes). So my current situation is I'm backfiring bad out of the intake where you can feel a knock on the dorkel. It's bad enough where I'm afraid to run it, thinking the whole manifold is going to fly off my engine like a shooting star. However, I'm going to try and adjust the TPS. I pulled it off when I took the throttle body off, and I'm sure it's screwed because I did that. Furthermore, I live in a jungle where we're full on summer mode with 100% humidity, everything is wet, and it just sucks to wrench or whatever. So, the saga continues.