Thread: 4L d2 rough idle, fuel smell, o2 sensor saga

My d2a 4L has never really idled well and is now returning 21l/100km. When coming to a rest, say clutching in to stop at traffic lights it will hunt for idle for a few seconds. It smells very fuelly. I had hoped it was the o2 sensors so i did a replacement with 4 wire NTK 0-1 volt units and did a conversion so that the car now uses v6 commodore o2 sensor plugs (i have not in any way touched the plug on the o2 sensor side, just the loom side that goes to the ECU). After replacing these o2 sensors i reset adaptations.

the rough idle is harmonic.. it isnt sporadic. The best way i can explain this is to say that it sounds like 1 or 2 cylinders are idling rough.. not all of them. The rough idle begins when engine reaches temp.

The sensors cycle from 0-1 volt (are they supposed to cycle down below 0.1v? because mine are doing that). I have driven around with the computer plugged in and the vehicle goes into closed loop and stays in closed loop, the fuel trims are working correctly and both bank 1 and bank 2 hover around 1 (fuel trims both fluctuate but never deviate to far from 1). the heater resistances are different though, whats with that?


The MAF is 6 months old, i also verified it with live time data and it seams to be working well.

I have replaced the purge valve with a good second hand unit in hopes that it was causing a vacuum leak.

all the plugs and leads are new.

no exhaust leaks in any part of the system.

throttle position returns home at 0% and looks to be working fine.

the passenger side (australian) breather tube is hard to suck are from)

the drivers side breather tube is very easy to suck air from.. it almost feels like the pcv valve is stuck open.

I do have a confession, I have used rtv sealant to seal the upper manifold though.. a propper gasket was 3 days away and i wanted to go camping. Is this a case that i need to go replace that with a gasket before coming back here?

Here is a snapshot from my diagnostics that show the car idling at temperature:



here is a photo of the codes recieved after a 3 hour drive:



I know this is alot of info to read through, but im just trying to give as much of background as possible. Please, if you think you might have any help to give let me know. i am able to get more screenshots of live data.

Originally Posted by Roverlord off road spares

x2 Yep those aftermarket sensors can cause problems.

These are NTK brand, i have heard good things about them. I made sure the wiring connections were hunkey dorey when i installed them. worse comes to worse i will replace them with factory units.