I just bought this 95 truck, and according to the previous owner the idle just recently (within the last two months) started surging. The odd thing is, it seems to happen most frequently when the brake pedal is pressed. If I set the parking brake only, the idle stays steady (seems a little higher than 750 rpm though).

I'm not much of a mechanic, but is this the idle control valve gone bad, or do I have a vacuum issue somewhere?

If it seems more likely to be a vacuum issue, how do I go about troubleshooting to find my problem?

I should also mention that the idle set screw will not budge.

 

The power brake booster runs on vacuum. If it has an internal leak, it will mess with the intake vacuum, which will cause surging.

Step 1: remove the booster vacuum line and plug the engine side. Does the surge go away? DO NOT DRIVE LIKE THIS. Whew! You need the booster to stop.

Step 2: At idle with booster connected, spray carb cleaner (or unlit propane torch) around booster line. If idle changes, could be vacuum leak.

 

I'll need a friend to step on the brake pedal to get the truck to idle surge (or a short pole or sturdy stick). So I assume there's only one vacuum line connected to the booster (it's dark and will look tomorrow). I need to remove it then plug the removed side (that would ordinarily be connected to the booster)? If the surge stops, can I assume the booster needs to be replaced? If not, it must be a vacuum leak then, right? I suppose using carb cleaner then would help me find my leak?

Just want to make sure I'm following you correctly.

Also, I live in California. Could a vacuum leak or bad booster affect the outcome of a smog check? I have a very short time frame to get this thing smog checked and completely registered under my name. And if it will affect it, I need to get it fixed before I try smogging it.

 

So I re read this, and I think I understand now. I need to remove the line completely and plug the engine side. Surge goes away, that confirms that the issue is located in that area. Replace the line, then check for leaks. If there are no leaks then I must have a bad brake booster.

But there is one thing that confuses me. If this happens only when the brake pedal is pressed, won't removing the vacuum hose essentially be like not pressing the brake pedal?

 

Well then.

Squeegee jammed in between brake pedal and seat.

Removed hose from engine side. Rpms drop significantly upon removal. Plug engine side. Rpms return to normal (surging).

Performed same test brake off. Rpms drop significantly upon removal of the line. Plug engine side, rpms return to normal (no surging).

I sprayed carb cleaner on every single vacuum connection, no change in rpms.

So I assume there are no leaks along the vacuum lines.

Do I have an internal leak in the booster?

I did notice while I was on the road (and stopped), I set the parking brake, released the brake pedal, and the motor started surging when normally it would not. This is new. It eventually went away.

 

It starts surging because the RPM is too high, and the fuel cut off is kicking in to drop RPM when the brake pedal is pressed.

My 92 22RE was doing it randomly, and after I replaced the IACV it has not done it since. Low coolant level can also cause it. Plugged IACV coolant lines can cause it. Change the idle set screw o-ring. Check for vacuum leaks.


http://htftp.offroadsz.com/marinhake...45fuelcutr.pdf

 

Ok well I checked for vacuum leaks and there doesn't appear to be any. And the idle set screw does not move at all. I even sprayed some liquid wrench on it still won't budge.

 

Somebody could have used some kind of sealer on the idle set screw instead of using a new o-ring. Get a micro torch from Harbor Freight, and heat the idle screw to get it off. Hopefully, it's not cross threaded.

https://www.harborfreight.com/butane...rch-63170.html

 

Here is how to check the Brake Booster:

 

I don't mean to be insulting, and please don't take this wrong, but were you trying to turn the actual idle adjust screw, or were you trying to screw in the cover screw over it? That confused the heck outta me the first time I went to tweak on the idle, after I replaced the head...twice. Long story. I didn't realize the screw that's visible is a cover for the actual idle adjust screw.

Notice removed cover screw

Did I read the book? Of course not. Real men don't read the book until their totally stuck. Everyone knows that
Yeah, I never claimed to be the brightest bulb in the string...
Pat☺

 

If the cover is slotted and metal than it's a possibility.

 

 

So I performed this aforementioned booster test. Everything checks out so I guess I can rule out the booster.

Thanks for the help guys...keep it coming..almost there. I'll feel relieved once I can figure out what needs to be fixed..with your help of course!

 

And torching the idle adjust screw got it to move ever so slightly, but it is super tight. Unfortunately I didn't notice any change.

So what should I do here? Halfway tempted to hit up a junkyard and just replace the whole damn throttle body. Of course I have no clue how much they'll want for it.

Judging by Ebay prices this is gonna be expensive. This truck looks nice but I'm starting to wish I hadn't bought it. Spent my whole stimulus check plus my paycheck. Now I'm broke and still haven't completed title transfer.

 

So..more reading...seems that this is a pretty common problem that can be caused by a whole slew of issues.

The radiator was recently replaced. I think tomorrow I'll try making sure that I bleed the coolant system so there's no air. Start with the simple fixes.

But further info seems to all point to the IACV..ranging from a dirty plugged hose to a full on cleaning of the throttle body and IACV. I was reading a thread on CarGurus that describes my issue to a T. Exact same symptoms.

 

If you do end up having to replace the IACV valve, Standard Motor Products Intermotor Genuine Import Parts AC141 is the same part as the Toyota part. Made in Japan, and RockAuto has it for $72.99. Mine did come with a new gasket in the box.

 

Yes, the picture above is the cover screw. Take that off to adjust the idle adjustment screw.
It's a real good idea, while in there, to pull out the idle adjust screw completely and check it's o-ring. They do deteriorate over time, and start leaking air around them. Changes the idle.
Pull the cover screw, and try to screw the idle adjust screw down until it stops. COUNT the turns you get it to make as you do, and then remove it. It's usually best to just replace the o-ring. They're cheap, and readily available all over the place. Auto parts stores, hardware stores, etc.
Put the screw back in with the new o-ring on it, and screw it down until it stops, then back it out to where it was before. It's just a starting point, and can be adjusted to set the idle correctly. I think you need 800 RPM for your particular truck, but I may well be wrong on that.

A little trick I found that helps the o-ring seal better, last longer, and screw in or out more easily, is to rub a little Vaseline onto it. A very slight layer. Only enough to coat the rubber entirely. Just a thought.

If the idle adjust screw is already down all the way, you may have another problem like IACV, or the o-ring gone bad and leaking air around it.

Good luck to you!
Pat☺

 

Its not coming out like it's a cover. There's no way to grab it anyway. It's also threaded. Are you sure a cover is threaded?

 

I don't have a cover on mine and there is no way a cover would screw in since the adjustment screw is pretty flush with the opening.
Here is a pic of the screw, looks like the one you are trying to remove...

 

This has saved me many times, but it would suck if you split the idle screw housing on the TB: