RPM bounces up and down after new o2 sensor

Howdy,

2001 prerunner v6 3.4 auto

CEL was on for bank 1 sensor 1 so I went ahead and replaced it and unplugged battery/EFI fuse to reset the ECU. Now with the new one in (

$137 Denso 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

Denso 234-9001) the truck bounces up about 100 rpm constantly at idle and even during acceleration. Ive only driven it about 40 miles so far so I'm wondering do I need to give it more time for the computer to relearn or is the part faulty/wrong?

Thanks

 

Was it doing this before you installed the new sensor? Usually rpm surging like that is caused by the o2 sensor 'hunting' for the proper air/fuel mix and is an indicator of a bad sensor. I'd give it about another 50 miles or so to sort itself out, but it may be possible that the other sensor is bad as well.

Another possible cause is a vacuum leak, but you should be able to hear it when you're under the hood. Plus, there aren't any vacuum lines that I remember near the O2 sensors so it's not likely you knocked one loose.

 

California emissions Tacoma? If so, then that part number is the incorrect O2 sensor.
Does the rpm actually change? Or does the needle just bounce?

 

Last I checked, 02 sensors report, they don't hunt.

 

It's a simplification, hence the quotation marks around it. Your Oxygen sensor constantly reports to the engine computer about fuel-air ratios and the computer makes adjustments based on them. However, mechanics refer to the surging caused from a malfunctioning or poorly functioning O2 sensor as 'hunting' because the engine bounces back and forth from too lean to too rich while it tries to find the right setting, which causes an rpm bounce.

 

A properly working O2 sensor ALWAYS bounces from Rich to lean, that is how it works. It is impossible for an engine to run perfectly at the proper fuel air mix at all times. This does not cause a fluctuating rpm or every efi engine out there would be fluctuating. Neve heard any mechanic use the phrase "hunting for the right mixture" and you can not always hear a vacuum leak.

Op, was it an actual code for the sensor itself or a generic lean code? If it just said lean it could be any number of things. If this problem just showed up with the new sensor though then it's possible the sensor has issues or it could just be a coincidence.

 

Yes, but a properly functioning O2 sensor lets the computer make adjustments in milliseconds, not in tenths, so you don't get bouncing in the RPM's.

And if you'll bother reading my initial response, it said "SHOULD" be able to hear a vacuum leak; not "WILL" be able to hear one.


But, it might be irrelevant anyway, since OP appears to have ghosted on all the followup questions directed his way.

 

Ok guys. I have the same issue. Engine light came on code is p0032.
P0032 code stands for “HO2S Heater Control Circuit High (Bank 1 Sensor 1).” I got a new sensor. The engine surges at an idle and acceleration. I unplug the sensor and engine gets smoother. Is it a bad sensor?

 

P0032 Toyota Code Meaning, Causes, Symptoms, & Tech Notes (With Video) (engine-codes.com)

The O2 and the maf sensors do a dance together to get that 14.7 ratio....
so first thing I'd do clean/inspect the maf and check its wiring...

if there is any vacuum leaks between the maf and intake valves....the engine computer is going to go nuts...
and there is alot places that can leak.......pcv/valve/grommet and its hose....brake booster is leaking...all kinds of places...

I'm not sure about exhaust leaks....whether it would mess this....but those are bad too.....cracked headers are common on 2000 and earlier....that cast iron does not hold up...

No1 reason for surging idles and throttling in these old tacos....is vac leaks.....rotten and wallowed out hose ends, that are no longer snug fitting..

dirty maf sensor is a close 2nd....


Eventually everyone gen1 is gonna need a smoke machine for various purposes...
$15 vacuum gauge from harbor freight wouldn't hurt either...

If you take it a mechanic.....alot of em will fire the parts cannon at it.....and still not even fix it...
and tell you to lump it....

 

Day of the necro post!

What O2 sensor are you using? All are not equal. And I agree with the prior post...vacuum leaks here and there add up. You may have disturbed old brittle hoses when changing the O2 sensor.

 

All the rubber crap on these are not milage dependent.....its age that gets em...

 

Absolutely. And none of it likes to be disturbed...at all.

 

Boy....you got that right....

thats reason.....Its a bad ideal to let anyone touch your monkey...