cpdjfd107

I got a CEL and it reads codes 1123 and 1125. Which is the left and right bank cyl 1-3 and 4-6. I did a search here but most topics are r/t 996 models. It could be the same as 993 but thought I'd ask here. Seeing they went out at the same time I am not thinking it is an O2 sensor problem (mine are new < 1000 miles) but it seems from reading this that the 02 sensors are reading a lean (or is it rich) mixture? So I am thinking maybe a vacuum leak or possibly a bad MAF. I replaced my Bosch MAF about 8 months ago (for no reason, just routine maintenance) with an ebay TRE-MAF. It said OEM quality but I still have a slight idle issue when I start the car from a warm start. It stumbles slightly where I have to give it a little gas to even it out. It doesn't do this from a cold start the idle is stronger when cold. It drives great and pulls fine. So please throw some opinions at me. Should I clean my old Bosch MAF and reinstall? I also have RS clutch and LWF but do not have stalling issues. My DME relay is new as well as fuel filter and all belts, caps, rotors, plugs, wires all good. Thanks for your help once again.

ilko

Cylinder layout:



Did you replace the O2 sensors with Bosch/OEM?

cpdjfd107

I just did the 2 pre-cat O2 sensors as I was to believe the post-cat O2 sensors are just for emissions monitoring and not fuel regulating. I ordered Bosch but ones of the O2 sensors said Borg-Warner on it. Maybe I should put my old Bosch O2 sensor back in and see if that helps? It read left and right bank 1-3 and 4-6 though, so wouldn't that mean that even if there was a faulty(Borg Warner) O2 sensor, the Bosch one also read the fault at the same time. Wouldn't only one of the codes 1123 or 1125 show up if it was just one O2 sensor? Thanks for your help, hopefully it will prevent me from removing a million things that I don't necessarily have to.

cpdjfd107

Bump. Any more ideas from anyone? I want to tackle this problem tomorrow if possible.

MarkD

Chris, those codes are often caused by the MAF.

I would clean and reinstall your OE MAF.
You will probably find that the idle issue goes away also.
My .02c

cpdjfd107

Thanks Mark, that's what I am hoping for. I knew you had all that info hoarded up!!!

MarkD

oh noo....

Slow Guy

Info constipation......

I would recommend cleaning it with a MAF sensor cleaner, I know CRC makes it and I'm sure others do too. I get it at the local Auto Zone.

rw229

As others have mentioned, start by cleaning your MAF using an electronics cleaner. Note that you will need to reset the CEL as it won't go out by itself after cleaning.

As far as idle, remove and clean the ISV valve (small cylinder on top of the intake). If never cleaned, it probably has some carbon build-up. (it should rattle when shaken)

cpdjfd107

Thanks for the ideas guys. I do a routine clean of my ISV so it shouldn't be that which is causing my idle issue. Hopefully it is the MAF. I mentioned earlier I replaced my 2 pre-cat 02 sesnors, but one was Borg-Warner, should I switch that one with the older (still functioning fine) Bosch one?

MarkD

Yes, definitely use a MAF cleaner
I wouldn't touch the o2 sensors, at least not yet.

Assuming the MAF is the fix, the idle issue will also be resolved
Please report back... I like closure

cpdjfd107

Will do Mark. Thanks again.

hoggel

I'd suggest you follow the advice of those with experience.

But if that doesn't work out ... The OBD manual says:

P1123 and P1125 "Fuel /air mixture is so rich that the control is up to the lean limit."
Fault area "-Fuel pressure too high. -Fuel injector leaking."

It suggests checking the fuel pressure, fuel pressure regulator, fuel pressure regulator vacuum connection, fuel return line, and the fuel injector for leaks.