My car's always been running without an O2 sensor since I purchased it. After fixing up the overheating problem, installed downpipe, no cat, FMIC, etc, car runs great except that, still no O2 sensor. My wideband tells me A/F at idle is erratic ranging from 10.5 to 15.5. From 2000 and above, A/F remains at the range of 10.5 to 11.5 at 1 bar boost which certainly is safe but I want more. So in goes a new O2 sensor but as soon as I got that connected, car idles horribly and die. I'm totally baffled as to why it even runs without the O2 sensor and why the new O2 sensor will cause it to die. As I said, car runs strongly at 1 bar and perfect transistion from primary to secondary. Please help if you have any clue.

Another sympton which might or might not be related is that Idle RPM doesn't go up when air con is on. In fact, RPM drops when compressor is on and engine died on several occassion.

Any comments at all will be much appreciated.

 

The oxygen sensor is only used at low RPM (idle). Above that the ECU has absolutely no care what the O2 sensor says because it's fuel maps don't take it into account.

If you have not reset the ECU, I would do that first. If that doesn't fix the idle problem I would work with the idle speed screw and throttle stop; it's possible somebody monkeyed with those to make the car idle when no O2 sensor was installed. You also mentioned the a/c idle problem. What ECU is installed? I know there were issues such as this with the Power FC.

 

the car is designed to raise the rpm to compensate for the extra load from the a/c compressor. so, the car shouldn't die. Plus rotory engine idles better when there is load applied to it.

 

the o2 is only used on crusing, not under decel mode, under X% throttle, under X amount of vacum.

Yes, you should try reset the ECU.

 

could this be my problem with sputterking at idle (very low and also dies) as well as when trying to be stable at rpms it sputters? accell and decell are fine.

 

A car running better with the O2 sensor disconnected is usually a sign of a bad 02 sensor. It is giving false readings to the ecu and the ecu is trying to compensate.

They are relatively cheap. Might as well get a new one. I got mine at oxygensensors.com

 

I got my O2 sensor new from oxygensensors.com. My car's ECU should have been resetted when I relocated the battery to behind the driver's seat but it hasn't been resetted after I installed the O2 sensor. The O2 sensor is said to be for a FD though the design looks quite different from the stock one. I don't suppose these things can't be mismatched if they all give 0-5V signal?

I'm running stock ECU but there is a small black box with some warning about electric fan operation that's spliced into the ECU loom which I haven't quite yet made out what's it for. I'm wondering whether the RPM is not raised when the A/C is on because there are piggyback devices that's bypassing the relevant signals. Does anyone know the sequence of events that cause the rpm to rise when the a/c is switched on? Does it rely on vacuum dropping or a simple matter of the a/c computer sending a signal to the main ECu telling it to raise the rpm?

 

bump

 

I resetted the ECU. Everything's fine now thanks.

 

I had my O2 sensor wire break off.

Car was stinking and the exhaust was getting black alot.

So I got a Bosch O2 replacement for $14 at www.kragen.com and it worked fine.