jsjensen73

I have a 91 runner with the 3vze. It starts up fine and runs ok for about 10 miles and then it losses power and has intermittent misfire/stumbling. I changed the TPS thinking that might be it. didn't change. Today I disconnected the O2 sensor and it ran fine, other then throwing a CEL. Any ideas as to why it runs better disconnected? There were no previous error codes.

Jrose

that is strange. Maybe you have a faulty O2 sensor and it's sending a bad signal. Have you tried replacing it to see if that fixes the problem?

jsjensen73

That's what i was going to do next, but thought it might be running lean with the O2 sensor. Causing the power loss and surging. Just looking for thoughts before throwing money at it.

dbd6604

You didn't have a CEL before you disconnected the 02 sensor?

jsjensen73

nope, jumped it anyway to be sure, but nothing before. Was driving down the road a couple months back and lost power. Could stay in 5th on flat ground. It was mostly in the midrange and the tps didn't read in spec so i swapped it, but no change.

dbd6604

This is kind of what I was thinking. Sounds like you're getting a lean condition that is causing the stumbling/misfiring, so when you unplug the 02 sensor, the engine goes into safe mode and throws extra fuel into the mix, causing the engine to run better. Clogged/dirty fuel injectors or a dying fuel pump possibly?

Keep in mind I'm no expert on the 3VZE, but I'm working on it.

jsjensen73

Yeah, its been an education this last year