joegoggans

My Check engine light came on, we pulled the codes, P1123 and P1125.
> My mechanic said we needed to replace the Idle Control Valve and the
> throttle position switch ( which I purchased from Pelican,
> 1415048923-080)
>
> My car ran fine before and still runs fine, but the Check engine light
> still comes on with the same codes. My mechanic said the computer
> still needs to learn the change, but its been two weeks and the light
> comes on every few days.
>
> This may be unrelated, but the horn does not sound when I set the car
> alarm, except when the check engine light is on.
>
> What are we missing?
>
> Thank you

mikefocke

– Incorrect signal from MAF sensor
– Intake air system leaking
– Fuel pressure too low
– Volume supply of fuel pump too low
– Fuel injectors fouled

It is considered wise to post the year of your car in your request for assistance as the codes differ depending on the year and knowing which ECU revision's manual to look at is helpful to the helpers. Any recent work done and any modifications done to the car also help.

How did he determine these parts need to be replaced? What instrument did he use? What flow chart did he follow? Does he have a Porsche diagnostic computer? Manuals?

extanker

i have little faith in your mechanic/parts changer

Macster

This may be unrelated, but the horn does not sound when I set the car alarm, except when the check engine light is on.

Oh oh. You need a young mechanic and an old mechanic.

Seriously, when I encounter seemingly unrelated things being possibly related I worry about water in car, in the cabin, at the security module (on the floor under the passenger's seat) or possibly at the DME located on the rear trunk bulkhead.

Yet another thing that can account for goofy electrical related gremlins is rodent damage to the electrical wiring. Mice are particularly fond of engine wiring harness wiring because it is so accessible yet hidden.

Let's see what the codes tell us:

P1125 - Oxygen Sensing Adaptation Area 1 (Cylinders 4 - 6) - Lean Threshold.

My reference doesn't list P1123 but I suspect it is the same problem just the other bank.

The DME has reached its limit in leaning out the mixture. The engine is running rich. This sort of explains why the engine is running so strong. The engine makes more power with a slightly richer than usual mixture.

You do not want to drive the car with the engine rich too much as the extra fuel can wash oil from the cylinder walls. This ain't good.

You can confirm the DME is attempting to remove fuel with an OBD2 code reader/data viewer by observing the short and long term fuel trims. If they are negative, that's the DME removing fuel (shortening the injector pulse times). Adjustments that get upwards of - (or + if the opposite condition was in effect) 10% is a pretty good sign something's amiss in the fueling department.

What can make an engine run rich? Too much fuel pressure is one such thing. A fuel pressure test could be called for but this is generally not a job for a home mechanic due to the risk of fire.

A low reading coolant temperature sensor or a low reading intake air temperature sensor can result in a rich running engine. A code reader/data viewer would let you observe these sensor readings in real time and possibly spot an obviously bogus reading.

BTW, the intake air temperature reading is a function of the MAF. A bad MAF therefore is not out the question.

It is hard to check out a MAF. One needs to use a test connector to gain access to the right pins to measure voltage and he needs to know pins to use and what the voltages should be.

A shade tree mechanic's test of the MAF is to disconnect it at the wiring harness and drive the car around normally and see if the same error codes come back. Now just because the CEL comes on you can't assume the same error codes are present. The MAF being disconnected can trigger error codes on its own.

Still on the subject of a MAF: Are you perchance running a K&N filter? This is often a source of problems with MAFs if the MAF proves to be the problem.

Be forewarned: You can't just run out and buy a MAF for the early model Boxsters. At some point Porsche switched to another MAF and the older MAF might not be arable and the new one won't work right unless the car's DME firmware is updated to accommodate the newer MAF.

Besides I'm not suggesting you replace the MAF. I suggest you replace your as extanker so succinctly put it "mechanic/parts changer" picking someone who can do the diagnostics that needs to be done to ID the source of of the problem.

joegoggans

Additional info.


1998 Boxster 2.5 , 35,050 miles.

Installed K&N air filter about 1,500 miles ago at oil change, changed all filters , oil , air, fuel and cabin.
The car has no smoke from exhaust pipe and it is not sutty black.

boxster newbie

maf is very sensitive, and problematic on these cars. most people, will tend to over oil a kn filter. probably sucks a bit of oil onto maf. pelican and other sources, say stick with stock air filter. also maf might be cleaned with spray or changed. read road and track, nov 2007, good article, includes these issues.

joegoggans

A tech at Pelican recomended I disconnect the battery and wait 30 mins. to clear the memory. I did this and the light has been off for two days now.

Also, since I did this reset the horn continues to sound when I set the alarm.

Macster

While disconnecting the battery for a time clears the error codes, it does not address the cause of the error codes.

This is disconnecting the battery is usually recommended when the error is suspected of being a glitch or just an issue arising from say leaving the gas cap off.

While it is possible I suppose the errors were due to some glitch I suspect this will prove to not be the case.

So when the CEL comes back on and the error codes have returned you have some things to look into.

Oh, the horn sounding when the car alarm is armed... I am not sure if these is a Komfort (Porsche terminology) setting. I prefer my cars to be quiet when arming the alarm.

If it is not a Komfort setting the horn sounding briefly when the car alarm is armed is a sign something is ajar. A door, a trunk lid, even the center console lid.

It can also be a problem with car's security system, or one of its components. In one case where my car was sounding the horn when locking the car the problem proved to be with the passenger side door lock assembly. (There were other symptoms too: the passenger window would not drop when the door was opened or worse yet drop then go back up once the door was opened. At some times the car would lock itself -- the red led at the lock button would come on concurrent with me hearing the doors lock -- when driving and I'd push the unlock button only to have the lock become active again on its own.)

A door lock assembly might be going bad in your car, or there can be other explanations. One that you should seriously consider is that water has made its way into the cabin. The usual path is from the water drain basins at the front of the car just ahead of the windshield. The drains can get blocked up and water can accumulate and overflow into the cabin. The water ends up on the cabin floor and it is on this floor, under the passenger seat where the security alarm module resides.

So, you should check for dampness in the cabin and along the doors. The 2nd source of water can be from inside a door. The door's water proof membrane fails and water builds up in the door and this water can then get into the cabin. The water in the door can also be the cause of the horn sounding.

PelicanParts.com

Please post back here if/when the CEL comes back on and if any other symptoms arise similar to the horn issue as well.

Great advice here so far for troubleshooting!

Mark/Pelican Parts

joegoggans

Pulled and cleaned MFS. Ran fine /great for 200 miles and light came back, but only got one code P1123. I have ordered a new MFS. I plan on installing this coming weekend.

mikefocke

Get rid of the K&N, clean the MAF. And the throttle body. Cheaper.

Mighty Shilling

Horn should only sound if there is something open- hood not latched, trunk not latched, door open, center console open. Otherwise it'll remain silent

Macster

There can be other times the horn sounds. When what proved to be my Boxster's passenger side door lock assembly was going bad the horn would sound when locking the car like something was open/ajar. I suspected it was the switch of the console latch and would open and close the console lid and this quieted the horn. But this behavior would appear again and again. Only after the door latch assembly was replaced did this behavior go away.

DennisAN

This is a very common problem over on the Miata forum too. "Oiled" air filters were designed for carbureted cars. They deposit oil on the MAF hot-wire and add a layer of thermal insulation to the wire so the MAF doesn't work right. The K&N worked great on my 1959 Austin Healey Bugeye Sprite. All it does is throw OBD-II codes on a modern car.

Note that K&N has spent great amounts of $$$$ trying to refute this problem.

mikefocke

And in a car mag test and one done by Consumer Reports the K&N let many more dirt particles pass and much larger ones, not something you want to be lubricating your bearings with.