I have a 2002 4Runner that I've owned since new.

It is completely stock.

It has about 138,000 miles now.

I've slowly noticed it is getting slower (lethargic) and worse mileage.

I am wondering if it's time to replace the o2 sensor or cat convertor to improve the mileage?

I have done all the scheduled maintenance and recently replaced the plug wires and plugs.

I think it's getting about 11-12 in town and 16.5 on the freeway.

Can someone recommend anything that may be causing this?

Thanks

 

I have 325,000 on my 01 and still have the original sensors and cat. I don't have any mileage complaints. It's been consistent throughout the years. The only time I noticed a drop off on performance was before an over due timeing belt change. I did have the exhaust system and throttle body cleaned out at around 275,000. When did you notice the mileage drop off?

 

Oh I do remember that the performance dropped off when the front O2 sensor bolts had rusted out and there was an air leak in the exhaust.