Check engine Light: oxygen sensors/ mass air sensor

[toyotaboy8]

hi
my check engine light on my 97 boxster reads P1123 and P1125 with the scanner. it pointed out to o2 sensors. i replaced all (4) 02 sensors and after 10 miles of driving, the light is back on and still shows the same codes. what do i do next? could it be the mass air sensor? thanks

mike

[Wayne 962]

Hi there. As I just finished writing in the new book the other day, a set of O2 sensor codes may or may not indicate problems with the sensors (most often, but not always). Sometimes it indicates a rich mixture situation that may toss O2 codes when they are not really the problem.

Did you replace the O2 sensors with original BOSCH ones with the factory connectors? I've had problems with the ones with the tap in connectors because the O2 sensors get their reference signal through the cable.

There are a few things that can cause a rich running condition. Yes, a dirty MAF may cause faulty readings and cause the mixture to go rich. Also vacuum leaks, like from the oil filler tube or elsewhere. A leaky EVAP valve can also cause this.

Do you have an aftermarket filter on the car?

-Wayne

[yupaleus]

I tell you what--i had an engine light problem--on, but my problem was also accompanied by an idle that went from 600-1000 rpm. I changed oxygen sensors, maf, all sorts of stuff. No luck.

I finally did a diy on the throttle body. I pulled out the throttle body, as described on another website, cleaned it out with some electrical cleaner, and to my shock and surprise, the idle problem was fixed and engine light was off, and has now remained off form months.

I'm not a mechanic--probably the hardest thing to do is getting to the engine. Then its a matter of just removing the big black air intake tube that goes to the throttle body, and unscrewing the throttle body with some allen wrenches. Also had to disconnect a wire. There was no more then just a 'film' of residue on the throttle body, not piles of dirt or anything extreme to the naked eye. I cleaned it up anyway, and the problem resolved. Maybe worth a try.

[Marks996]

I have similar problem on 99 996. p1123,1125 and sketchy idle around 6-800rpm

[Emery G.]

Mass airflow sensor is usually the culprit for faults p1123,p1125. The sensors see a rich/lean mixture because the mass airflow sensor is sending a signal to the dme to go rich or lean. there are preset limits in the dme maps for rich/lean conditons. If the mixture goes above or below these limit the check engine light will iluminate. A hunting idle could also be a vacuum leak.

[Wayne 962]

Here's my just-released article on the Mass Air Flow sensor (MAF), and how to diagnose problems with it:

Pelican Technical Article: Troubleshooting and Replacing the Mass Air Flow Sensor (MAF) - 986 Boxster (1997-04) - 987 Boxster (2005-08)

(still working on the formatting)

-Wayne