Quite often that idle fluctuation is due to the idle being too high. The ECU is designed in such a way that if the idle is above 1000 RPM, I think it is, the ECU shuts down the injectors when the brakes are pressed. They figured that if the engine is above the max RPMs when brakes are pressed, you're slowing down, and you don't need the engine pushing hard against that. Once the idle drops below the maximum, it allows the injectors to function again. If the idle is set high, the ECU will again cut off the injectors, the idle drops, it allows them on again, the ECU senses the RPMs are too high, it cuts the injectors, etc, etc.

The idle RPM should be set to 850. Use an external tach to set the idle, not a tach built into the vehicle. Once the idle is set correctly, check the timing. Make sure the timing is correct, and check the idle one last time, once the timing is set correctly.

I won't swear that this is the trouble, but it sounds like it to me. Ok, I will swear, a lot, but I am a former Marine, so it's just a bad habit I have.
Pat☺

 

thanks for the input, super valid tips. Although in this case my timing is spot on where it should be and the idle is set to spec. So I’m back to believing I have a leak in the booster, which is original to the vehicle so it is it a far fetched idea. To appease the Toyota gods I will pull out the gun and double verify my timing this weekend.

 

Second gen 4Runners with the V6 have a dual diaphragm booster which will add a good bit of boost over a single diaphragm booster. Second gen 4Runners are a dime a dozen and all over every pull-your-own junkyard. I've used them as a source for brake boosters a few times and always been happy. They swap right in, just make sure to adjust the pushrod correctly.

 

so the booster i have on hand that was for a v6, i believe came off a v6 2nd gen pickup. and unfortunately here in louisiana toyotas do make it to parts yards, and if they do the south of the border workers are usually at the door before it opens waiting to strip it. also, ive read alot of guys have trouble fitting those boosters without "persuasion" form a brass mallet. any knowledge on that?

 

Never had any clearance issues. Bolt on. I believe they were original equipment on our generation of trucks if they had a V6 or 22RET. I have the same setup on both my trucks.

 

i used a t100 dual booster on my '86 4runner... there might be two different t100 boosters, slightly different diameters? https://www.roundforge.com/articles/...booster-specs/
https://www.pirate4x4.com/threads/br...grades.132252/

the big diameter boosters hit the steering column on 1st-gen pickups, so be careful there.

i had to take it back off and remove the firewall spacer :-/ so be sure and check the pushrod distance before putting the mc back on... my pushrod is barely long enough, wish i knew where to get a longer one.

while you are under the dash, be sure and check the foot pedal bracket for cracks.

i swapped the mc also, and went with the slightly bigger rear slave cylinder, ac delco was cheaper than toyota: that's the correct landcruiser replacement, see the comments... i do have the v6 rear axle.

 

thanks, i have already done all the other upgrades you mention and yeah aftermarket is always cheaper but, you get what you pay for. i dont see many parts store parts lasting 30 years or more.

 

i had a cheap clutch master fail on me, went toyota for that part.

this acdelco 1" i.d. slave cylinder is not that, it's their pro line, with a 2-year warranty, while the cheap versions of it have a 90-day warranty: https://www.rockauto.com/en/catalog/...+cylinder,1952

the toyota version is $39 at marlin, no specified warranty: https://www.marlincrawler.com/brake/...wheel-cylinder

 

@arlindsay1992 ,
Thanks for info on the vacuum booster.
Does it have to come with matching master cylinder?
Pretty much any second-gen or V6 1988 4Runner? I get intermittent "notch" feel on the brake only when engine is on, so I do not think it's mechanical binding. More likely something to do with the vacuum boost. It doesn't affect stopping so I;m waiting to get replacement booster ready before I take things apart.

Thanks for your service, Pat!
That same G#$$@*$d Sh&t happened on mine, too. [LOL!- I'm a former sailor, Desert Storm on USS Tripoli LPH10, the one that ran into a mine ]
When AC was on and came to a stop at freeway exit it would hunt. Lowering to proper idle fixed it in a second.

 

Thank you for YOUR service, Rad! I remember that incident. Glad you were safe wherever you were aboard the boat.

Amazing what a small, simple adjustment can accomplish, sometimes, aint it?

Have fun!
Pat☺

 

If you have a 1" bore master cylinder already, no need to pay for another master from the junkyard, just make sure the pushrod is adjusted correctly. However, if you're planning to do this swap for the first time, buy the master and booster together at the junkyard. Often the Pick Your Part places have a separate line item for booster and master as a unit which is cheaper than the prices separately. Also, you will not need to adjust the pushrod since the booster and master were adjusted for each other at the factory. This only applies to factory Toyota parts that are original to the vehicle, of course. I've had good luck with used OEM brake parts from the junkyard, not so much with rebuilt stuff from the parts stores. The rebuilt stuff works fine when new but they usually only last a couple years before springing a leak or some other weird thing. Toyota stuff lasts decades.

 

Thanks!
Mine's stock so probably not 1-inch. Absolutely about OEM.

 

Buttoned this project up today. I decided to take some measurements on the FJ62 booster I had, and behold! It fits. Same bolt patterns. The FJ62 does use the spacer on the back, and I had that also. I had to play the guessing game with the push rod a bit because I don’t have the SST but after 2 tried I had it right. I won’t go into detail in that here, there’s lots of thread son who to adjust them. So all in all, I now have the larger V6 calipers and rotors, FJ 60 rear wheel cylinders, V6 master, and FJ62 booster. Hope this helps at least one person.

 

Great thread and i’ll refer back to you when i do mine!

one note about pushrod length i can add since i have been through this on my 67 Camaro when upgrading to discs. If brakes feel grabby or drag and get hot your pushrod adjustment is too long.

A change of .030” on the pushrod will feel significant at the brake pedal.

 

I meant to add these part numbers, both gaskets and the nuts with attached washers for the booster to master studs.

 

Thanks for keeping this thread so thorough.

As far as pushrods go, thats a really good point. When installing the master, you shouldnt have to force it onto the booster. If you do, the pushrod is already pressing the brakes. If this happens, you will smoke your rotors. I saw a car on the road a couple nights ago, rotors orange with sparks flying off them. Not safe.