The 4runner is running rough when I start it up. I think it probably needs a set of plugs. What's the best? BTW it needs an O2 sensor, would that make it run rough on start up?

 

Best plug is the OEM NGK or Denso.

O2 sensor could make it run rough but if the throttle body needs cleaning or IAC is sticking, MAF is dirty, dirty air/fuel filter, etc could all cause similar symptoms.

 

So do you think I should start with the plugs and go from there? It has 145,000mi, and I'm not sure when they were changed last. I've only had it for about 6 mos.

 

I would start by doing a basic tune up, plugs, air filter, fuel filter and clean the throttle body.
I bet the idle will be very smooth after that.

 

I have Iridiums...but that was by accidental shipment by URD.
I would go with NGK's or Denso's.

www.sparkplugs.com has a good selection and ratings of them for your year model.
I also picked up my NGK Blue sparkplug wires from them for less than $30 and love them. I strongly recommend them if it is time to replace your wires.

For your 1996 here are the recommended plugs:
http://www.sparkplugs.com/results_ap...1&AAIA=1272574

And for the wire set they have the NGK's for $27.76

Also the O2 sensors for your model also ranging in the $90 range, not sure how good a price that is.

Good luck!

 

I think URD (Gadget) had the OEM sensors cheaper (for an O2 sensor I would ALWAYS use an OEM part).

 

How often should the oxygen sensor be changed? How many miles is to many?

 

NGK plugs

 

Mileage will really depend on many factors but if it were my vehicle I would replace it for sure if my vehicle had over 100k on the same sensor. I have seen them fail as early as 80k but some may go well over 200k. If you want to ensure maximum gas mileage, it is a good idea to replace it.

 

This is a quite a range. Are there symptoms to tell if you need to change the oxygen sensor? What are the symptoms? It doesen't seem like mileage is a good rule of thumb to use. Hope I'm not hijacking this thread.

As far as spark plugs go I use Bosch Platinum 4 but I will try iridum plugs next time around. I heard bad things about Platinum 4 on the 3.4L.

 

The check engine light will tell you when to change it.

 

Isn't it possible for the oxygen sensor to fail and not have a check engine light on? I belive the oxygen sensor can pass the diagnostic test at start up and still send a bad signal to the computer with out a check engine light.

 

You'd need to buy an OBD tool like the ones below (for which you'll also need a laptop or PDA) in order to view the actual signal from the O2 sensor in real-time, that is the only way to tell if it is still doing its job. Even then it is difficult to tell if the O2 sensor's response is slowing down enough to lose gas mileage but not enough to throw a CEL. To answer your question, yes and no......yes, the sensor can become slow or have reduced performance without giving a CEL and no, if it does fail completely, it will throw a CEL at you. This is why most of the time mileage is used for replacement if people are concerned about maximum MPG, but if you prefer only to fix when broken, wait for a CEL. Your call.

OBD II tools:
http://www.auterraweb.com/
http://www.obddiagnostics.com/

 

I agree and I might just add that the front sensor (before cat) is the one that effects the ECU tuning and would be the most important to have in good condition. The rear sensor behind the cat just tells you if your cat is working up to EPA standards and I'd wait untill it throws a CEL before replacing it.

My 97 BMW 328i has dual exhaust so it has FOUR O2 sensors so what I plan on doing is just replacing the 2 front sensors now and wait for a CEL to do the rears.