Hey all. Recently purchased a 92 4Runner (3.0 with the Auto Trans) . And overall, I love it. However, with any 30 year old vehicle, there are some issues. Would anyone be able to help me out with the following?

- There seems to be one (Or multiple) Vacuum leaks, Idling can a bit rough, and I can tell the engine is struggling to maintain power. When the A/C gets turned on, Idling gets worse and has stalled a few times. Last owner replaced most hoses, and there aren't any obvious cracks. Any tips on finding the leak? Once it's on the road, it seems fine until I get to a stoplight. (yes, the head gasket was done recently)

- I also have Transmission concerns. Approx. halfway between 1000 and 2000 RPMs, things get "Jumpy". It seems to function better with Overdrive Off, but that may be placebo. No other obvious issues in other gears, and the trans fluid looks and smells fine.

- Lastly, after coming home from a drive, I hear an intermittent "Pop" come from below The under carriage. Air filter is decently clean, not sure about anything other than that.

My only thoughts are potentially the Fuel Regulator, or the EGR. No check engine light, and it passed AZ emissions when I bought it. So i'm trumped. Do I just have to deal with the headache of finding the bad hose? Any tips on doing that?

 

Welcome to YotaTech.

The usual way to search for vacuum leaks is with an unlit propane torch, or a spray of starter fluid. When propane/starter fluid hits the vacuum leak, the engine speed will change (up or down; it depends on how close the mixture is now.)

One of the vacuum switching valves on the right apron (engine bay) is the A/C idle-up. When the A/C is on, it admits atmospheric air into the plenum, raising the idle. You might try to test that.

You'll need to refer to the sticker under the hood for all the vacuum connections.

Lots of things can cause rough idle. At a minimum get a $30 timing light and check the ignition timing. You can also use the inductive pickup on each plug wire; if the light flashes, the plug fired. You might find a poor plug wire or plug out of spec. You can try a "cylinder efficiency test"; pull the plug wires one at a time. If one doesn't change anything, that cylinder isn't doing anything.

 

Don't assume the vacuum lies are routed properly. After this many years there's a a good possibility something is routed wrong. Those emission piping schematics seem busy(and they are) but if you focus on one line at a time they make sense.
You might do a compression test. If everything is strong, and all six cylinders are pretty close to each other you can move on. if any seem off than do a leakdown test. That'll help you isolate the possible cause(say a tight valve)

Curious. Is the air filter a regular one, or one that requires oiling?
Are sparkplugs, cap, rotor, wireset Toyota or Denso? Plugs would be my biggest concern.

Does the fluctuating rpm's seem to hit a specific rpm?
Also, Might be worth changing atf with a known brand. If the previous owner used the chain parts store "house brand" that may affect shifting performance

 

upon inspection, I'm starting to think some hoses are routed incorrectly. One line has a bolt capping the end of end of it. Time to label and go through each one! The plug wires look like they're in pretty good shape, I'll have to check the gap on the plugs themselves.

- As far as RPM goes, it sits around 1000 RPM on startup, and goes up to around 1200 upon shifting into drive

- I've had the engine stall every time I reverse out of a parking lot with The A/C running. It starts right up again, but it's an annoyance.

 

I also removed the idle air adjustment screw, and found the end caked in black deposits, it also adjusts a bit too easy.Would it behoove me to clean the throttle body and check the TPS?

 

I'm assuming it's been running like this since you purchased the vehicle.
I'll also guess that the previous owner tried some things to remedy, or maybe tried to do some work that caused it.

So, you need to get things back to spec as much as you can, and pretend someone has been there before and did things wrong. Timing set wrong, vacuum piping wrong, TPS set incorrectly, etc. You also need to look at basic tune up parts and see if they bought inexpensive(albeit new) parts to see if they could find a quick fix. If sparkplugs are anything other than ND(NipponDenso) or NGK get rid of them. Bosch are particularly poor performers in Toyotas. I prefer plugs that have solid terminals, not the screw-on ones.

Compression test wouldn't hurt. Good basic info to have.
I've posted before on how to set TPS with a timing light. Never tried it on a 3VZE, but I'd think it'd be the same. Worth trying. If it doesn't work you can always do the multi-meter method.

Look at the distributer adjusting bolt. It should be pretty close to center in the adjusting slot. If it's close to the end of the slot that could indicate they had problems setting timing.
Same with TPS. The adjusting screws should be kinda close to center, also. Maxed out to either side would be odd.

 

Updates: Replaced the plugs with NGKs, which helped acceleration and power, but made Idling worse. Engine has a surging idle ONLY after coming up to temp, and it sounds "Puffy" when surging, you hear it lose power and fight to come back to normal idle. Had the vacuum checked out for the third time by our family mechanic, and he didn't find anything obvious. I'm suspecting that the "Shifting" concern is actually a stuttering engine between 1300-1700 RPM. Here's some more data to hopefully help diagnose:

- All of the old plugs looked normally worn, nothing out of the ordinary. Plug wires and rotor looked fine.

- We did a quick thermostat test on the cylinders while up to temp, and cylinder one only read around 250 degrees, while all others were around 350-400.

- The engine likes to stall when I'm taking a sharp turn out of a parking spot.

- There has also been two times where the engine has stalled after starting *both times the engine was already hot from a previous drive*. My band-aid was to pull out the screw a bit to increase the idle, but I'd like to find the cause.

Any advice from the toyota wizards?

 

Spray brake cleaner on the vacuum hose ends while the engine is running to check for leaks. If the engine RPMs pickup you have a leak.

Make a DIY smoke machine with a cheap soldering iron, an empty pickle glass jar (or similar), a vacuum line hose fitting to fit small clear hose form Home Depot cut to desired length, and baby oil to smoke. Mine make a ton of smoke. I needed it to check for an exhaust leak.