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92 Toyota 4 runner project - Engine idle issues both cold and warm. THIS is NOT just a simple leak!

Hello, My problem with this truck is that I cant seem to get ride of it. I have had it since high school and will probably always keep it. With that said I have been getting it back on the road and let me tell you this has been a challenge.

Its a rebuilt engine done by our mechanic who is very good at his job. Great guy all around but being that he is just that, he stays very busy and for him to hunt down this problem has proven to be very time consuming for both of us.

PROBLEM: The truck runs strong, engine feels better than ever but the idle is loping beyond anything I can describe. This doesn’t start right away, and from the start the engine starts cold really well. Idle seems high but more along the lines of the old “choke” feeling on the older trucks. After a few min the idle levels out still a bit high due to us running it that high so it counters the loping that seems to start at the warm temps. ( The TPS thing is “hunting” I guess they call it. Seems to never find a happy spot)

Once the truck gets driving down the road its fine and there isn’t any loping. The loping seems to start once I shut off the truck after a few min of driving in town, and then restart it a few min later. 9 times out 10 the truck will start and immediately start with a very low and loping idle which continues on until I let the engine cool.

This loping effects the brakes as I have to stand on them at a stop light so the truck doesn’t carry on into the cars ahead lol. The brakes do feel like they have some extra play in them but that could also be they are old. Sometimes its so bad that I have to put it in neutral and the engine idle drops and calms but not completely. Giving it gas ( as to kick off the choke again in the older trucks) seems to do nothing much, at times I feel it might change the loping but doesn’t effect its presence.

I just picked up the truck again today as my main car is in for repairs and talking with the mechanic it would seem that this issue is going to take a Toyota 4 runner whisperer. Someone that has had fun with this issue in the past and tracking it down. The mech has gone through the vacuum lines, the master cylinder and cant seem to find the leak or if there is even one. He said today he can usually hear a leaking master so he doesn’t think its that but its not ruled out yet.

I really don’t know where to begin. I know my way around just fine, I don’t however have much expertise with vacuums. Googling around has gave me some ideas and good ones, things like throttle cable, TPS, and the like. I thought Id reach out to some people who might be able to get me headed into the right direction with this issue. I love this truck and i cant get rid of it. Its my toy and has most recently become a new hobby of mine.

One last easy question I’m sure gets asked a lot… Truck is old, was kept up well and maintained. To get the truck running smooth down the road ( drive train wise ) what should o start looking into changing? Things like shocks, new tires, wheels, new suspension all around, struts and things like that ?

I know this is a very long post and because so many responses today that I see, they tend to be wasted with ( could you give us Xyz info plz) so I try to include all I can think of.

Thanks again for taking your time to help me with this or any info offered for that matter. If i have posted in the wrong area it was not intentional and I apologize.

Thanks again,

When you say ‘master’ do you mean the brake booster. I am wondering if you have a flaky booster. This would be the source of the vacuum leak and the lack of vacuum brake boost. Try clamping off the hose going to the booster to see if the lope changes. Don’t drive it this way as you may have even worse braking ability

BTW is this 4 runner carburated or fuel injected with idle air control assembly. I don’t have access to Alldata at this facility

Yes, im sorry. The brake booster, and we just ran some tests on the vacuum preasure and its pretty low. Cant seem to narrow it down to the booster though. Thats the third person today to point towards the brake system, so guess thats where we should focus. Thanks for the heads up on driving it. From what we can tell everything is routed right and no missing hoses.

The truck has the 3VZ-E v6 3.0 EFI and uses a throttle body type set up. Hope that helps. Ill check back in when i get home

Thanks so much by the way.
Swapz, Casey