1999 SL-2 rough idle

Pete, check all sensors and sending units (or wahtever thier names are these days). On my 2000 SL1, the ECM temperature sensor went bad, and caused the ECM to declare a small vaccum leak. Took a few trips to the dealer before they found that the temp sensor was corroded. The clue was rough and high idle speed (thanks for the tach, I could tell them that bit).

Thanks..........I will give it a try.

Pete

OK to answer your question, the O2 Sensor has to be located between the Exhaust port and the catalytic converter on all OBDII cars. Some have a second one after the catalytic converter, yours does not I think. Usually it is located close to the engine on the exhaust manifold because it requires a certain amount of heat before it will function correctly. Before it reaches the operating temperature, the system operates in a specail fail safe mode using factory set perimeters and will (possibly) run rough due to the fact that it is not real time adjusting the Air Fuel mixture. For a decent explaination of the O2 sensor, see this link

Now, You have a '99 Sl-2. From my memory, that O2 unit is directly on the Exhaust Manifold. Open the hood look straight down between the engine and radiator. The O2 sensor sticks out to the drivers side of the exhast manifold (the rusty piece of metal coming off the front of the engine and turning down). There is one wire going into this unit if I remember ciorrectly, but you need to know the wire count when you go to the store for a new one. Also, while you're there, borrow their O2 sensor removal and installation tool (if they don't have a loaner for this go find a store that does, it makes the job easier). The Saturn wiring snaps off the back ( I think you squeeze the connector) of the old sensor, you unscrew and then reattach the new sensor.

As someone else wrote, you may not have a bad O2 sensor, I'm guessing you are seeing code P0153. Check out this link.

Code in the computer is just based on what it sees. What it istelling you in this case is that "I sent the signal for more oxygen tothe intake manifold circuits, and I did not see a corresponding changein the O2 sensor signal that I expected." The cause can be air gettinginto or out of the exhuast manifold, another sensor dumping too muchfuel into the engine, a manifold air sensor that is malfunctioning,etc... The OBDII codes are nice, but they won't do the work for you,they just tell you what to start with, you still have to do somedetective work. The first thing I would do is inspect the exhaustmanifold for any cracks, maybe crank the engine and see if you can heara sound leak around the front of the engine where the exhaust gasesare maybe leaking. Past that change the sensor and see what happens.Good luck.

One other note, at 80k that sensor maybe a little tough to remove. If it is start the engine and run it jsut for a second to heat the exhaust manifold slight. The metal will expand a little and often unstick a stuck bolt/sensor/spark plug. Be careful not to get burned.

Pete KE9OA wrote: