Idle still not smooth after O2 sensor replacement

[Sal]

Hi everyone. So I had a CEL w/P1167 code on my 02 Accord 4-cyl 190,000 miles. Idle was rough and RPM’s would dip low. Did some research and this most commonly meant the pre-cat O2 sensor was toast. I replaced it with the correct Denso part as spec’d on their website since these ULEV engines are very picky about which sensor to use. CEL’s now gone, RPM’s are solid but the idle still isn’t as smooth as it used to be. I feel vibrations in the steering wheel and dashboard and there is this faint groaning/moaning from the engine. Vibrations oddly seem to be worse when in park. Before the CEL coming on, the car never did this before. Spark plugs are NGK plats and not that old. Front engine mount is OEM Honda about 1 yr old. Car still pulls strong without any hesitation. I unplugged the battery for an hour hoping an ECU reset would help; no change unfortunately.

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[none]

I’m thinking vacuum leak since it idles rough but runs well at speed.. If you have something that’ll let you read the fuel trims, you’d be looking for the trims to be adding a lot of fuel at idle and returning closer to zero trims while throttling the engine. You don’t need to even drive the car while you throttle it and you don’t need much more than 1500-2000 rpms while you’re testing.

[Brian]

I’ve had this issue on more than just Honda cars. Turns out it was a slight carbon build up on the throttle body butterfly and the area just around it.

https://youtu.be/41yFXjibtLY.

[zero]

For any car with a cable controlled throttle body, a good cleaning won’t hurt anything. If your car doesn’t have a MAF sensor, you can even clean the throttle body and then run the rest of the can through with the engine running. Beware, it absolutely stinks.

I would check the condition of the plugs, wires, cap, rotor etc.

[Sal]

Cleaned out the TB this morning. Wasn’t too dirty as I had cleaned it previously 20,000 miles ago. No change in idle quality and the faint groan is still there. I added a bottle of Techron Concentrate Plus to see if it’s a fuel-related issue. The idle doesn’t surge and when I rev the engine to 5K RPM, it returns right back to around 700 RPM without dipping too low first. This leads me to believe the IACV is fine. I sprayed around for possible vacuum leaks and arcing of the plug wires to no avail. Car starts up fine in the morning without hesitation with a cold idle of about 1250 RPM initially. The external seal of the distributor appears to be leaking oil (common on these cars). There’s dried oil on some connector right below the distributor. Not sure if that’s the coolant temp sensor or what.

Wish the CEL was on so I could at least pull a code for something 🙁

[Author]

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