Changed the primary o2 sensor today due to a check engine light. Ever since it was changed this morning, the car is idling weird. It's my Wife's car and it's an automatic. We've had it for 70,000 miles, so I know it very well. It used to always idle at 800 rpm when fully warmed up and in park. Now once it is warmed up and in park, it goes from 1,000 all the way back down to around 200rpm and nearly dies, but surges back up to 1,000 and then it repeats itself. If you are at a light and have it in drive with your foot on the brake, it idles normally.

What could be going on? I'm about ready to just burn this car to the ground lol

 

Did you reset the ECU and do the idle learn procedure?

 

No I didn't reset the ecu. I didn't even think it was needed?


These symptoms remind me a lot of a bad IACV. I had an old DA that did this. It's a huge issue with DA Integras, but I've never really heard of it being an issue in an Rsx.

 

It sounds more like a bad IACV for sure. If you can reach it unplug it once and see what the idle conditions change to.

If it idles high but even probably a bad or dirty IACV... If it just falls flat on its face it could be a vacuum leak instead.