• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Renix lowish idle


NAXJA Forum User
Peabody, MA
I have been plagued with a low "ish" idle problem for a while now. I have a new rebuilt engine with 11k Miles on it. Runs fine and idles smooth just low. Around 550-600. And sometimes almost stalls or stumbles. When cold started it idles up fine and once warmed it sits low. All sensors are reporting correctly as I have read the ecu data.

Throttle body is clean and there are no vacuum leaks. There is a bypass screw on the side that was closed all the way. I adjusted out a smidge and the idle went up. Then the ecu corrected it and brought it back down. So I set that back.

Also when the ac is turned on it idles up as it's supposed to.

The only thing I'm questioning is possibly the o2 sensor. It's new but it doesn't always like going into closed loop on the first shot. It will go closed loop. Before it's swinging and will start dying and pop back into open loop and recover.

I have done battery cable upgrades and ground upgrades and cleaning.

88 xj

What's the best o2 sensor? Bosch? And what exactly is the idle speed when in gear? Or park?
Had similar symptoms, ended up being the EGR. Try pulling the vacuum line and plugging it and see what happens. NTK is the best O2 sensor for the Renix.
i did have it disconnected and plugged for a while. in the summer its not really an issue and i think that's when it was plugged. i did take the egr apart and cleaned it. should the pintle move at all at idle?
If you have everything connected, blip the throttle and you should see the pintle move.

You can also use a small blade flat screwdriver to lever the pintle open when idling. The RPMs should drop, maybe even stall.

I run NTK O2 sensors now as I always seem to have a bad O2 (Bosch) by the time I get back to smog testing.
I have nudged the pintle and it has stalled. I have the vacuum line capped at the moment and nothing has changed.

I recently replaced the O2 with a NTK I believe.
I recently picked up a Picoscope so I've been playing around testing sensors. My idle kind of surges a bit and I noticed that the surge directly lines up with the O2 switching from lean to rich.
i disconnected the egr for a while and was noticing the engine started pinging. and did nothing for the idle.

when it is idling the Short term fuel trims are really low. and most times when it goes into closed loop in the morning when its cold it almost dies. ill try unplugging the o2 and seeing if it makes any difference with idling.