MAF - Mass airflow sensor - located inline with the intake downstream from your air cleaner. Detects how much air is flowing into engine - signal tells engine how much fuel to give for proper A/F ratio

O2 - Oxygen sensor - located in the exhaust manifold. Tells engine lean/rich condition based on exhaust gases and works with computer to adjust mixture to correct.

 

Regarding computer box, does anybody knows how to remove the computer box and where it is located?
Thanks.

 

The PCM is located under the radio but it is not likely to be bad. It would be rare anyway. Try cleaning the MAF hotwire.

 

For two days now, my car engine runs ok without doing anything. I have not try driving in the city street yet, instead in our company's compound where I used to keep my car.

At normal idle speed, rpm meter reads 900 and will drop to almost half when I try to shift to drive position.

Same thing happens when I switch on the aircon, rpm reading drops to half.

It seems that the idler up sensor is not operating normally.

Is there a way to test the idler up sensor?

 

I don't know about the idle up sensor, but can suggest something that can cause rich mixture and didn't throw a trouble code in my 94 mx3 4 cyl: Coolant Thermosensor. There are two temp sensors, one for the dash gauge, one for ECU. If the ECU thermosensor is faulty, the ECU never 'knows' the engine is warm and doesn't lean out the mixture. It can be tested with an ohm-meter or any multi-meter. Mine ended up being broken (not sending signal at all), so it ran rich and eventually fouled the plugs.

 

Idle up sensor is the one that raises the RPM once we switch on the aircon compressor to compensate the drop in RPM.It is mounted on the side of the throttle body itself.Rough idle now comes occasionally,not like before and no more smell of gas. By the way,where is this ECU thermostat located? Many thanks for all your time and support.

 

I can only relay the location of the thermosensor on the DOHC 4-cyl MX3: close to distributer, and was the highest mounted sensor in that area. the harness only contained 2 wires. When it was broke, my plugs would foul, reek of gas, and wouldn't run well at all. changed plugs, and it did well for a while, before they fouled out again. repeat till i finally studied that sensor. hope that helps...

 

Many thanks for all your help and support Rough idle associated with varying RPM reading appears most of the time. But there are also times that it is normal.Still locating the reasons for this. Anyway thanks for all your help.