I have a '94 4Runner 3VZE, MT, 4x4.

I've been having an ongoing problem with my truck which has the following symptoms:

- After driving for a while -- it varies, but it can be as long as half an hour (so well after the engine has reached normal operating temp according to the dash gauge) -- the engine will start losing power and eventually stall entirely. There are no symptoms of overheating.

- After driving for a while, if it either stalls or is turned off on purpose, it won't start and stay running until it's been left to sit for half an hour or so (It does crank, but either won't catch at all or lugs for a few seconds and dies.)

- Once it has been off for a long enough time, it starts right up again like nothing is wrong.

- At any time while driving, it has occasional "hiccups" on acceleration.

- The CEL is NOT on, but there is a stored code 14.

- The problem has gotten worse (i.e., shortening the duration it can run without stalling) over time.

There are two potentially-relevant weird things about the truck (that I've noticed, at least):

- The previous owner installed an Amsoil bypass oil filter.

- There's either JB-Weld or gasket maker between the throttle body and the intake plenum.

I've looked through a bunch of forum threads here and elsewhere for other cases with similar symptoms, but the answers have been so varied I've only managed to confuse myself. Some of the more popular suggestions include the idle speed control valve or the intake air temperature sensor, but I've also seen guesses about pretty much everything from vacuum leaks to a bad ECU.

I also tried taking it to two mechanics:

- My usual trusted mechanic is reluctant to work on it for some reason and thinks I should get rid of it (he says I'd be better off swapping it for a vehicle with ODB2, even though he has no qualms about working on my pre-ODB2 Miata...). Nevertheless, he spent quite a few hours trying to diagnose it and fixed a problems with a disconnected wire and a hole in the exhaust header. He made the problem better for a while, but it still exists.

- I tried taking it to another local mechanic today who suggested it might be the fuel pump when I described the symptoms (and seemed sure that it was not the idle air control valve with the reasoning that that should only affect idling), but he's too busy to look at it until at least Thursday, so I thought I might take another crack at it figuring it out myself.

Any suggestions?

 

we had the same problem for years on my sons truck .. and I replaced everything it seemed , and it still persisted .
he took it to a mechanic where he lives a few times , and I even suggested replacing the fuse box , didnt do that , but replaced all the fuses .
still the same !!
I persisted in my pursuit of the problem .. in looking at the wiring diagram , there is a fusible link directly from the battery to the fuse box , white 8 gauge I believe it was ....
anyway , replaced it , and problem solved .
it may have been a few problems , and not that one specifically .. but maybe try it .

 

Sounds a lot like a bad (even disconnected) ECT sensor. Here's the test procedure: http://web.archive.org/web/201411140...98engineco.pdf The ECT sensor is in the "water bypass" at the back of the engine, along with a bunch of other sensors. The ECT sensor is a 2-wire sensor.

The better test for a fuel pump problem is with a fuel pressure gauge, but that requires the gauge, adapter, and some assembly. A useful and quick almost-as-good test is to replace the fuel return line from the FPR with 1/4" hose to a suitable container. Start the fuel pump with the FP-B+ jumper (key-on). There is no spec, but I get about 1/2 liter/min at idle. Increasing the rpms (fuel demand) should reduce that flow; if the flow goes all the way to zero your fuel pump is not maintaining sufficient pressure.

The fuel return line is low pressure, so you can disconnect it by releasing the simple clamp. The high-pressure side of the fuel system is sealed with crush washers. Those are one-time-use and must be replaced each time a connection is opened.

 

If anybody cares, it turns out that replacing either the MAF sensor or the fuel pump fixed the major stalling problem. (I'm not sure which was the true culprit because the shop changed both at the same time.)

Some of the slight hiccups on acceleration remain. Between that and the general sound of it (which might be totally normal, for all I know, but doesn't sound what I would call "good") I'm still not 100% confident in its reliability, but it seems to be okay to drive now so I'm loathe to mess with it for a while.

 

Glad you solved your problem. Mine started the hiccup thing at 103,000 miles and it still does it occasionally at 370,000 miles. Also, when my MAF crashed, the engine would start and run for about two seconds before dying. No mechanic has touched my truck since 2000, and I had one tell me he wouldn't touch any vehicle made before 1996 so chances are that the earlier model Mazda made use of some type of diagnostic unit that was available before the ODB2 came along for the Toyota truck. With minor problems repaired, you should enjoy your truck. Good luck.