I had a problem with vibration at idle and rough idle when car is warmed up. I've researched all youtube video finding similar symptoms people have and there was guy who had a same symptom as I have and he figured out with O2 sensor. He didn't have any error code or check engine light.. me as well. so I bought the NTK O2 sensor for replacement from pepboys and while i was driving yesterday, check engine light came on and scanned with the scanner and error code was P0136 which is bank 1 sensor 2. I had replaced with cheap one from amazon a year ago and i think it went bad so soon. anyway today I replaced downstream one with NTK O2 sensor but symptom is still there.. and I captured live scan obd tool by my iphone and realized that upstream sensor 1 was not stable. I captured this video at idling after car is warmed up. Is this normal or something's wrong? maybe header went bad as well?
Please advise. Thanks

 

 

That's good then. One thing i forgot to mention that is when car is warmed up, rpm is not stable and rpm is quiet low around 700-750 and makes vibration. when rpm automatically goes up to 800, car feels normal but it holds only few moments. rpm goes down to 700-750 again. Even ac is on, there are a lot of vibration going on. this is so weird...

 

You may want to do a simple compression test. My R50 had very similar symptoms and it turned out that I had 2 burned exhaust valves. One had a very visible crack in it and the other had scoring all the way around the valve seat this was across 2 different cylinders.

Before anyone jumps in saying a compression test won't find burned valves, they are correct. It won't point at a valve issue, but it will tell you that something is wrong in that cylinder and that you need to investigate further. Also, compression tests are very easy to do, especially on an R50.

 

I did a compression test about a week ago.
the result
#1 140 psi
#2 125 psi
#3 140 psi
#4 130 psi