Wes Whitmore

So I have been watching my CEL come on and go off on it's own for the past year now. All of my V6 trucks and this 4runner have done it. It is staying on much more than it is off now, so I think it is finally time to fix it. I am interested in getting one of those 02 sensor testors, but thought maybe I could do some "desk" troubleshooting while I am here at work.
First off, everyone talks about pulling the battery to reset the CEL. Why does mine go off by itself? I can understand why it stays off when you reset the battery(whatever caused it to turn on isn't occuring at that time), but what about one that resets itself?
I still have the original MAF sensor, but I don't think that is the problem. The thing runs great, and has only very rarely had a slight idle fluctuation that drops the RPMs 300 RPM or so, kind of like when you turn on the AC. It always bounces right back up. Consequenty, it's when I am sitting at a light that the check engine light usually comes on. It's on 90% of the time now though. The engine isn't always warm when it happens.
The exhaust still stinks. Smells "better" with higher octane gas. Still stinks though. I have no idea if the cat is plugged up, but I do know that I am on original O2 sensors with 127,000 miles. I get plenty of exhaust air coming out of the pipe on a cold morning, but that doesn't prove much about the cat, does it?
Any general discussion would be cool. I just need some help getting started locating the problem.
Thanks guys,
Wes

Unhappy99

a) what year is your vehicle?
b) what code is actually being generated?
c) from what you describe, this happens routinely on
99+ models, and its likely a dirty MAF. Clean it.

CEL will go on and off by itself. If the ECU sees two consecutive out of spec errors, it lights the CEL. If it sees three consecutive OK trips, then it turns off the CEL.

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MenaceSQL

When my '89 truck had that on and off CEL problem, it ended up being the O2 sensor. Actually the exhaust pipes fried two of the O2 sensor wires so it was tripping the CEL. BTW, on my truck, I don't remember if it was in the owner's manual or the FSM but it said to replace the O2 sensor at 80,000 miles.

denverbikeguy

Just wondering but what is a good cheap place to find the OEM O2 sensors for say, a 97 V6 4Runner? Any kind of discount is welcome. I hate paying dealer prices.

Pretacopower

Mine started doing the same thing....CEL came on and off by itself and I didn't think much of it since the thing ran fine. Then one day the CEL was on and my truck stalled at a stop sign. I then decided to take it in and it turned out to be my throttle positioning sensor, needed to be replaced. Happened at about 79,000 miles.