Hi all, I'm new to this site so please bear with me. I just recently bought a 2000 Mazda Millenia S, Miller cycle engine, and have been having trouble finding the root of some problems while trying to pass emissions . The car has just about 100k miles. Recently my check engine light had been throwing the codes of an O2 sensor failing. After just having taken it to a Midas for some small maintenance, I filled the car with a 91 octane gasoline. The previous owners had run 82 octane in the car and had kept it in good condition. On the drive home from filling the car with 91, the check engine light came back on along with the TCS off and TCS light as soon as I started going up a hill. After turning the engine off and on, the lights disappear and the car drives fine, but while the lights remain on, the car jerks at and will not exceed 2500 rpm. After turning the car off, there is also a pungent smell. As soon as I drive this gas tank off, I'm going to fill it with 87 and see if the problem persists. Any ideas as to what the problem might be?

 

sounds like you have a problem with your abv. if the check engine lite is on, you probably have codes 1525/26 and 1540 stored. possibly 0725. there are several places to start, but if you have those codes, you need to check the vacuum/vent solenoids, and the vacuum lines and tees in that circuit. the car is in limp home mode

 

Thank you for your help! I also should have specified that the work done at the shop was on the vacuum lines, was just wondering whether the gasoline had anything to do with it, probably a silly question. Thanks a ton!

 

Also, can the O2 sensor be replaced without replacing the whole catalytic converter?

 

of course. 2 separate entities. but changing the sensor wont cure the cat codes(0421/31). if your shop is telling you that, dont go back there. actually, and i have been criticized for saying this, if you cannot do a lot of the work on the car yourself, get rid of it. it will eat your lunch. and dont expect to take it to a shop and have them fix the problem, because one of the main problems is that most shops have never even SEEN this engine before, let alone have any experience on it