Rough Idle + 'too lean' and 'too rich'

SBUS01

MEMBER
1993 TOYOTA 4RUNNER

I have a '93 4runner, 3VZ-E V6 with 4WD and 5-spd manual.

Some history:

Head gaskets were replaced 2X; the 3rd time they replaced the heads with 1997s. Ran great for years after.

I blew ANOTHER head gasket, replaced it (one side only) along with the knock sensor (they broke that off when working on the head) and also 2 fuel injectors (they said they were plugged when working on the head).

Current problem:

Recently it started running like the head gaskets were blown, extremely rough, no power, etc. Although sometimes (usually at freeway speeds) it'll suddenly start running fine. But:

1. No steam/antifreeze in the exhaust.
2. Good compression.
3. OBD codes are 'too rich' and 'too lean'.

After these symptoms started, I failed smog and replaced the EGR valve, smog pump, pre-cat O2 sensor, and the cat converter. I also found a plugged EGR hose and fixed it, passed smog.

Same symptoms.

I replaced the knock sensor (again) since someone suggested it might be defective and it was under warranty.

I gave it a tuneup (replaced plugs/wires/cap/rotor).

So here's what's been suggested:

a. Bad ignition module
b. Plugged fuel injector
c. Car is simply a piece of sh*t

Any ideas? I believe the rich+lean codes are the clue; but haven't been able to find anything to fix.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

There are a couple of things we need to start with when checking for this issue. First and foremost is a vacuum leak.

Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If there are no leaks, then we need to test the EVAP system for the TVV being clogged or stuck open. This is a thermal vacuum valve and if they stick open then they are allowing vapor from the canister to come into the engine when they should not.

Please see the info below for detail on this. Please run through this info and let us know what you find.

Thanks

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