Hello, I have a 1999 996 C2 6-speed with 91,000 miles. Only mods are a K&N filter, headers, and an old K-40 radar detector hard-wired into the DME. I bought the car about a month ago for a steal at $9,000.00 because the engine light was on and it had a rough idle. I was hoping for some help with diagnosing its problem(s).
Symptoms:
1. rough idle - rumbles like a muscle car and sometimes idles is at 700rpm and sometimes at 1200rpm.
2. Difficulty starting about 1 in 5 times. Requires excessive turn over and priming with more gas.
3. Poor mileage - 12-13 mpg
4. Sometimes smells like it is running rich
5. Gas tank won't fill to Full; it never shows above 7/8 tank.
6. Check engine light is on most of the time, but occasionally goes off for a day. Usually goes on when I'm in higher rpm's.
7. Very tiny intermittent oil leak coming from passenger side front of engine bay.
Codes:
1. P1539 - Camshaft adjustment bank 2 (4-6) Frequency 166
2. P0446 shutoff Valve Activate Charcoal Filter; Frequency 2
3. P1124 Oxygen sensing range 1 Cyl 1-3
4. P0455 Tank Ventilation (Major Leak)
My thoughts so far:
1. Air oil separator causing vacuum leak, causing it to think it's running lean, and then overcompensating by enriching the mixture, hence the P1124, rough idle, problems starting, and intermittent oil leak.
2. Camshaft problem - I'm not sure there's a problem with the camshaft actuator itself because I great great performance from the car in all rpm ranges; it pulls great above 3k rpm so you'd think performance would be affected if it were unable to adjust. That leaves either a bad sensor, a problem with the DME from the K40 radar detector, or something in between.
3. Fuel tank may be a purge valve issue, blocked vent tube, or the fact that the k40 intentionally causes the gas cap light to turn on when it detects radar and this in turn caused the error. The K40 cause still wouldn't explain the inability to read "Full" on the gas gage.
I'd appreciate any input and/or differing opinions!
P0455
Leakage in fuel tansystem
Diagnostic conditions
Vehicle speed = 0 km/h
Engine speed = 0 rpm
Correction factor, height > 0.73
Coolant temperature upon starting the engine may be no more than 6.8
above ambient temperature
Coolant temperature when engine starts > 3.8 °C
Period for which the engine needs to have been running before ignition
is switched off > 20 minutes
Ignition has been switched off for at least 10 seconds.
Ambient temperature 4 … 35.3 °C
Active charcoal filter load < 3 for minor lea
Fuel tanfuel level 10 … 54 litres
Battery positive voltage 11.02 ... 14.5 V
No fuel tanfilling
No faults detected for ambient pressure sensor, coolant temperature
sensor, vehicle speed sensor
No output stage faults detected for DMTL pump motor, DMTL switch-
over valves and tanvent
No fault detected for tanvent (flow)
E The diagnostic conditions can also be established using the PIWIS
Tester via the short test "tanleakage test". After the test has begun, the
ignition must be switched off.
NOTE
In this context, please also observe the function description.
Possible fault causes
Tancap not closed correctly, leaking or missing
Purge air line leaking
Tanvent leaking
DMTL (TanLeakage Diagnostics Module) leaking
Leakage in fuel tansystem
Function description
Tanleakage test/DMTL – TanLeakage Diagnostics Module
Note
The tanleakage test is performed only on USA vehicles.
Construction of the tanleakage diagnostics module:
The diagnostics module consists of an electric motor with a small air
pump, switch-over valves and a reference nozzle.
In addition, the modul is heated so as to prevent the forming of
condensation and ice.
Procedure of the function:
The pump is operated via an electric motor and conveys air through the
reference leak. The power consumed during this process is determined.
The switch-over valve switches and the air current is now directed into
the fuel tank. The power consumed during this process is also
determined. After a waiting period dependent on the fuel tanfuel level, it
must be at least as high as the power consumption was during the
reference leatest if the tansystem is leak-free.
The system is identified to by leaking if the power consumption is lower
during the actual leakage test as it was during the reference leatest.
An evaluation of the power consumption levels when the pump is
started and after the switch-over valve has switched serves to identify
faults within the tanleakage diagnostic module (e.g. pump blocked,
motor spins at idle speed, valve does not switch etc.).
The diagnosis of heating, motor and switch-over valve is performed via
the output stage of the DME control module.
Hope that helps, I didn't have the other 3 codes listed but I don't have the DME codes for 1999 handy at the moment either.
Thanks for the reply K-Man. I've heard that the P0455 is usually a purge line / vent blockage.
Do you think the AOS may be the culprit for the P1124 and the symptoms I described? I'm having second thoughts considering that only cylinders 1-3 were affected with the P1124 (and no P1126).
For the P1539 my guess is the VarioCam solenoid/actuator on that bank is bad. Just went through this with my 02 Boxster (at around 240K miles).
Engine runnnig just fine then pulled into work parking lot and engine got rough. I thought maybe a gas line came loose or fuel low and fuel pump sucked some air (though I never run the fuel tank that low). Nearly same symptoms as you report. Very muscle car like though scary and obviously not a healthy idle.
Long story short pulled the error codes and they pointed to the VarioCam hardware. Oh, checked fuel trims and engine controller running the bad bank rich to try to compensate for the failing solenoid/actuator.
Had the VarioCam solenoid/actuator replaced (engine stays in the car, at least with my Boxster). $1500 parts (roughly) and about the same amount of labor.
To get to the solenoid the exhaust manifold has to come out (tech told me a bolt snapped -- common and the shop budgets for at least one). Camshaft cover comes off. To get to actuator cams come out. Much more work too but I can't give you the details.
Lots of new seals, seal plugs, and new camshaft cover bolts. Do not reuse the old ones. Tech (at a Porsche dealer) used a special sealer. Camshaft cover has no gasket. The cover is the top of half of the cam bearings and experiences alot of oil pressure. Proper prep and sealer application with correct tightening sequence and new hardware will see the cover oil tight.
Sincerely,
Rockster.
K-Man s gives the very good and descriptive solution . Thanks for sharing your knowledge with us.
Well you've got a real mixture there of faults, but Variocam would seem to fit most of it and realiability of the Variocam on the 996 and 986 was not known to be the most reliable. :cheers:
