Well, one final test run to the supermarket with the O2 sensor plugged back in. From the off it idled bad, was bucking again and losing power to the point I thought it was gonna die on me! This is worse than it was before the unplug. After returning to the car, it almost didn't start up again, just turned and turned (I gave it a bit of gas and it fired up).

Readings at idle after warm up were much the same - maybe a little higher in range.



I'm in the UK (our forums aren't as forthcoming or knowledgeable) and we don't have AutoZone.

It's gonna take me about a week to get a new NTK sensor as I'll have to eBay it. No one else seems to stock that brand and even if they did it'd be double the cost of an online purchase and even an online purchase is about double what you can pick them up for your side of the pond!

I'll report back when fitted.

 

For what it's worth, it seems Rock Auto will ship an NTK 23121 for €38.99 after discount code to Manchester (no idea where you are so I picked a random city)

 

I'll give that a go - I'm not far from Manchester, good guess! And thanks for the part number.

You guys are too helpful

 

I know the drill with getting parts... retail automotive stores in Canada are not an experience for the working folk

Random discount code from RockAuto 5387936748131651

 

He's Canadian - he picked up the Brit vibes.

 

Actually I went with the first hit from Google for UK postal codes, Manchester was the first in England (no self respecting Scot, Irish, or Welsh would say "UK") that my eyes landed on. Total luck lol

 

So, after a bit of a wait...

The new NTK O2 sensor turned up yesterday. I installed tonight and went for a drive for a few miles.

Early indictions look good. Vast improvement with idling, no stalling or bucking and consistently smooth running. Idling isn't perfect, but then it is a 20 year old motor with 116k on the clock, so I don't expect it to be.

Had a look at the live date from the scan tool after engine got up to full temp, and it look a lot more like it should do. Again, not a model chart, but I think near enough. STFT is back within range. LTFT is a bit high, but maybe that will change with use. Only time will tell.

A couple more runs from cold will confirm if I've solved the bad idle and bucking issue.

 

Oi, that's a lot more like it isn't it.
One word of advice, clear out or reset your pcm codes, it will start recalibrating the fuel trim memory tables from default. Otherwise it will eventually get it right but you want to not confuse it too badly by just sticking in the new O2. If your tool doesn't have that function, just disconnect the battery for a half hour then reconnect.

 

Great advice, thanks. I can clear codes (already have done) but don't think it will have re-set the PCM, so will do the battery disconnect at the weekend. Then I can move on to all the other gremlins that need ironing out but I'll get there. Love a good project, but more so in the summer.

If this turns out to be the fix, I'll be preaching. I've seen so many rough idle/bucking/stalling threads and so many people seem to have thrown so much at it to fix, but to no avail. The only ones that ever seem to solve it are those that have replaced the upstream O2 sensor - so by deduction I started looking at that before going down more expensive routes.

 

my 00 ran smooth with a bad o2-2 at cat. replaced it and cleared code, no difference in very good running 4.0,,,gutsy!

 

Clearing the codes, even if there aren't any, is sufficient. That will reset the monitors. If in doubt you can check the monitor readiness function before and after you clear codes. You will see a few not ready after, those will 'run' as you drive.

 

Excellent! Looks much better

And yes, the PCM will continue to use LTFT in calculating the engine's fuelling. LTFT is based on something like 20 or 30 drive cycles, and of course, will be based on bad data from the old sensor. Killing the power to the PCM and making sure the capacitors drain is the only way to reset that data without a DRB-III tool. After reset it will fall to a factory 'guess' based on a theoretically healthy engine.

 

Ah, well this seems to contradict what I just said. Could I be wrong? I admit that has happened a couple times.

 

Yeah it just resets the readiness monitors, not all of the PCM's adaptive memory.