Rep Power: 0

I bought a 2001 Honda Civic EX. 1.7l Vtec.

I've had surging idle issues since I bought it. When It warms up fully, the throttle is jerky. It's either on, or off.

I've gone through:
- Ignition Coil (cyl 4, just in case)
- New Plugs (cylinder 4 misfire, the plug was fouled. The rest were fine.)
- New IACV
- PCV
- Throttle Body cleaned.
- New vacuum hoses.

It's throwing a code for the downstream O2 sensor. The catalytic converter has been removed, and the sensor cut. I believe this is the source of the idling issue. Has anyone else had this specific issue? I am debating whether to just buy a new catalytic converter and downstream sensor and see if that is the issue, or if there is a "flash" or "tune" that could correct this. That leads me to ask, are there any specific remedies for this issue that doesn't involve buying a cat?

Update: 1/12/23 - I got the non-fouler and O2 sensor mounted into the down pipe. It got rid of the CEL, but the idling surge remains. It doesn't activate the CEL, but it's still P0505.

Update 4/2/23 : I replaced the throttle body with an OEM one, fully dressed. It had Denso sensors, and it also had the bottom of the butterfly valve cleaned. Usually, there is what looks like paint at the bottom of these, this one had it entirely cleaned. I don't necessarily know if that is an issue or not. But It completely fixed the issue. ALSO, with the p0505. the transmission would not shift into first gear, now that It's idling normally, first gear is back.

tl;dr OEM fully dressed throttlebody.

 
Rep Power: 513

First off, it may be purely coincidental that idle issues and the cat delete happened at the same time. Correlation ≠ causation kinda deal. With the sensor being cut.. where is it cut? Between the sensor and the terminal where it plugs in, or on the wire harness side of the terminal where it plugs in. I'd hope it's on the sensor side of that terminal.
Here's visual reference (cuts indicated by //):
[sensor]----//-----[terminal][terminal]------[rest of wiring harness]
or
[sensor]-----------[terminal][terminal]----//----[rest of wiring harness]

Nevertheless, with no connection to that sensor, yeah, it'll throw a code for that sensor because the ECU is seeing it as missing. With no cat and that sensor properly connected, I'd imagine it'll throw a P0420 code (catalyst system under efficiency threshold). You can solve that with an O2 simulator (or do the "mechanical O2 simulator" spark plug non-fouler trick: https://www.civicforums.com/forums/7...simulator.html). I can attest that the mechanical O2 simulator works and passes an OBD smog check.

you may want to try an idle relearn procedure and see if that alleviates your idle issues.

 
Rep Power: 0

Thank god, it's just the O2 sensor itself that was cut. The wiring harness is still intact.

I will definitely look into doing the mechanical non-fouler.

 
Rep Power: 368

then just get new sensor and non-fouler

 
Rep Power: 223

Try cleaning the iac

 
Rep Power: 0

I cleaned the original, no change. Then I replaced it. It's not a cheap amazon one either.

 
Rep Power: 223

Is it a cheap autozone one?

 
Rep Power: 0

It was $180 from O'Rileys.

 
Rep Power: 513

try an idle re-learn procedure and see if it fixes it

 
Rep Power: 0

It has not. I've done the re-learn periodically once I thought the issue was fixed.

 
Rep Power: 368

Editing the first post will confuse people...
Just reply to the thread.
Reset Codes once and idle relearn again

 
Rep Power: 0

I've reset the codes and performed the idle relearn multiple times. It has not fixed the issue.

 
Rep Power: 513

might be time for a vacuum leak hunt. Those aren't fun to find