1993 Toyota 4Runner

Engine Performance problem
1993 Toyota 4Runner 6 cyl Four Wheel Drive Manual 200K miles

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.
February 4, 2009.

Hi sbus01,

Thank you for the donation and the history which is helpful to understand the situation.

There have been instances of such symptoms and the cause is a contaminated Mass Air Flow sensor. The contamination gives a false signal to the ECM thus the lean and rich condition.

This is quite a common phenomenon and a special cleaner was formulated to clean the sensor. You can try asking at your local parts outlet for the spray cleaner.

Feb 4, 2009.