Surging Issue
 

All,

I need some help. I've got a 2000 4Runner, 3.4L V6, 4WD, 4.10 gears in the rear end (according to Toyota when I do a VIN number lookup) and California emissions with 212K on the odometer that I bought on 12/31/18. It's started giving me a weird surging (engine revs up by about 200 RPM and then drops back down to where I was holding the throttle) while driving. The issue occurs regardless of speed in the 1900-2200 RPM range. It does not occur while in park or neutral. It also has zero power on the highway. The thing has all kinds of hell trying to stay at 70 MPH on the highway.

The air filter was replaced and the MAF cleaned with CRC MAF cleaner at 209K miles.
Oil was changed at 209K. Oil level is good.
Fuel filter replaced at 209K.
Coolant leel is good.
ATF level is good. I do not know when it was changed last. I haven't gotten to it.
I put in new NGK plugs and wires at 210K.

The issue began around 3/2/19. Since then, I have done the following:

212216 miles - replaced the TPS with OEM part.
212698 - replaced fuel pump with a Denso 950-0100, new fuel pump tank seal and replaced the fuel filter again.

When I was replacing the fuel pump, I did notice that the gasket after the primary catalytic converter has a leak.

Any ideas on what I should look into to figure this thing out?

Thank you!

It's not the floor mat. I double checked. And then I pulled it out and went for a test drive, just to make sure. It's still doing the surging thing. It's almost like it's not getting enough fuel. It's driving me freaking insane!

Struggling can be caused be either side of the motor. Either not enough air/fuel/spark is coming in. OR the cat is plugged and spent gases can’t leave the motor. Can you split the bolts before the cat? If your cat converter is plugged it’ll act like an engine brake.

Also, are you sure it’s motor related and not say a stick caliper or bound up u-joint?

will it rev freely in neutral? Or is it crapping our under all load conditions?

It'll rev freely in neutral or park. The surging issue only occurs in gear between 1900 and 2200 RPM. When in gear, it will rarely go above 2800-3000 RPM.

I haven't tried pulling apart the bolts in front of the cat. I haven't gotten that far.

How would I check for a sticky caliper or a bad u-joint?

I've got a bit more info to add. I had a co-worker go to lunch with me today, so I had someone that could keep an eye on the OBD Fusion app on my iPhone while I was driving.

The surging issue occurs in all gears where I can hold it between 1900 and 2200 RPM. It's worse in 2nd and 3rd than it is anywhere else, but it occurs in every gear.

When the surging occurs, the Bank 1, sensor 2 O2 sensor voltage drops down to the .1-.2 volt range. When I gas it to get out of the surge, the O2 sensor reads between .6 and .8 volts, depending on how much I'm on the throttle.

The exhaust leak is apparently getting worse, as it is louder today than it was over the weekend.

No codes showing as set or pending at this time.

Anybody have any idea on what I should look into?

Problem solved. I replaced both cats, the A/F sensor and the O2 sensor. Engine is running like a sewing machine now. And the fuel economy has gone way up (21.1 MPG yesterday with mostly 70-80 MPH Highway driving).

Excellent news, thanks for reporting back:)