CEL & P1123 P1125

[WC Cowboy]

The car is a 1999 996 C2 Cab 6spd US non turbo 43K miles DME has 5.2.2 software bone stock. I have a Durametric tool and I get the CEL and codes P1123 & P1125 once reset they will show back up between 250-2500 miles. Here are the idle DME measurements with top down and everything in the car turned off. I have all the repair records for the car and nothing major has ever been done to it. I far as I can tell all the engine parts are orginal. I have a K&N air filter in the factory air box it is not over oiled and the MAF and the airbox have been cleaned properly and showed no signs of grease or dirt within the air intake portion. Code P1123 will usually show up first followed by the CEL a little later and then P1125. City driving (idleing) seems to bring on the CEL quicker. So I am looking for some help on what it all means. I'm leaning towards a faulty MAF or possibly the EVAP canister valve.

Load Signal = 1.6ms (a little high maybe)

RPM = 680

MAF = 19.25 Kg/h

Hot Film = 1.31V

Ignition Timing = 5.9 (varies wildly from 4.5 to 9.0 on the Durametric tool trace/chart/graph)

Spec, Air Mass = 20 Kg/h (a little high)

Spec. Air Adapt. = 4.0 Kg/h

Injection Timing = 2.6 (a little low)

I have always considered myself a fair mechanic but this is my first adventure in computer diagnostics. The car runs just fine, it has a good stable idle even with the compressor cycling. It has plenty of power and is a real nice car. I know this is just a minor emissions code but still do not want to see that CEL on. Nor do I want to keep driving and resetting (ignoring) the CEL. I have been trying to learn what I could and get the right tolls for the job but I am at the point where good friendly advice is my best option. Any reply will be greatly appreciated. One more thing the O2 sensors are responding normally from what I can tell and have been told to look for. The K&N filter did help lean it out some but obviously not enough. What else should I be looking at?

[JFP in PA]

Generally, these codes are related as they indicate an overly rich condition (P1123 for bank 1-3, P1125 for bank 4-6). Common issues are too much fuel pressure (possible fuel pressure regulator) or one or more injectors leaking.

I'd also be concerned about your MAF value, 19.25 Kg/Hr seems like low air flow, more used to seeing around 29 Kg/Hr. You may want to carefully look at your intake system for blockages or constrictions, and perhaps give the MAF a cleaning.

[hiteck]

Had these 2 codes on my '99. Replaced MAF sensor.

[kbrandsma]

I had these codes and others as well. Replaced the gas cap. Mine is a MY98 and it had an orginal gas cap. The new ones have the leash which I find helpful. I then replaced the change over valve and these two(2) codes went away.

Always a good idea to reset the codes with durametric tool and drive a couple of drive cycles between any repairs. Good luck and let us know how you resolve the codes.

[Ahsai]

All your sensor reading seems fine at idle at least. What are the readings at crusing @3000rpm? Also, what are the short and long term fuel trims at idle and at cruising? Also, can you read the freeze frame data, which can tell you under what conditions the codes were triggered.

[WC Cowboy]

I had these codes and others as well. Replaced the gas cap. Mine is a MY98 and it had an orginal gas cap. The new ones have the leash which I find helpful. I then replaced the change over valve and these two(2) codes went away.

Always a good idea to reset the codes with durametric tool and drive a couple of drive cycles between any repairs. Good luck and let us know how you resolve the codes.

Change Over Valve? Ar you by chnace refering to the EVAP Canister valve?

[kbrandsma]

No, on the Boxster it is called a changeover valve.