99 4runner SR5 4x4 144k miles
6 cyl
Colorado location in case this matters.
Started to run poorly last summer. Check engine light came on
Cleaned the MAF Ran great and light would actually go off from time to time.
Fast forward a year later
1 Week ago, started rough running.

Rough idle and poor running at normal acceleration.

Had codes checked and got
Lean bank 1
MAF
Random misfires

Replaced the MAF and checked codes again
MAF gone, but random misfire and misfire on cyl 3

Replaced Plugs
Replaced Wires
Replaced Coil Pack on cylinder 3

Pulled negative wire and left off for entire process. (??Does this clear codes??) I don't own the code reader the local autozone does. Is there a safety mode that the car runs in until a code is cleared and removing a cable doesnt fix.

Smelled gas from exhaust more pronounced than usual.

Unplugged O2 sensors and started car. Exhaust smelled better idled better.
Ran without 02 plugged in. Same running issues.

Where should I venture next. Possibly a fuel injector?

Maybe just to the mechanic would be the logical step instead of throwing money at possible ideas.




Mat

 

I'd replace the O2 sensor

 

Both or 1 at a time and if so which one.

Why wouldn't it throw a code for an 02 sensor and still continue the code for misfire on 3 or random misfire.

Mat

 

I would just do the front first, if you have 144k on the truck it should be changed anyway. You said it ran better w/o it plugged in, that leads me to believe it's the prob.

 

Welcome to the "Randome Misfire" Club. My 97 (with engine #2) is doing the same thing, but I'm constantly getting a Misfire in Cyl. #2. I've done everything you did and still no change.

Let me know how the new O2 sensor works.

Bob

 

Check for a vacuum hose leak, I had some crazy codes nothing would clear. It finally got really rough at idle when I found one of the hoses off the top of the engine had a small tear.

 

I would replace the front O2 just because it's due anyways (don't worry about the rear, it doesn't affect the running condition, just monitors the efficiency of the cat) and test the injectors.