CEL Durametric shows P0150, P0507, P0446

[P2C4]

1999 C4, 145K miles. I've owned it for 6 years, since 37K miles. Has ran well, driven daily, and well maintained. Currently it is half way through it's second tank of gas that included the big bottle of Techron. I run a tank or two of Techron through it every 5K miles before the regular oil change.

CEL light came on, and Durametric software shows these codes:

-- P0150 Porsche fault code 18 -O2 sensor ahead of cat. conv. (cylinder 4-6)

-- P0507 Porsche fault code 32 - idle air control system, exceeds limit valve

-- P0446 Porsche fault code 95 - shutoff valve activated, charcoal filter (function)

Air filter is standard Porsche, and was replaced 1K miles ago, and Mass Air Flow sensor cleaned at that time, and throttle body as well.

Searching this site i find some helpful information about the 0150 and 0446 codes, but nothing on the 0507, or this combination of Codes.

Your suggestions will be appreciated. Thanks.

[logray]

Interesting combination of codes.

What does the car idle at ? I bet it is high.

What are the fuel trims at ?

Is there an intake leak (p0507?)

Also have a look at the throttle body and make sure it is not binding (you should have egas, so unlikely).

If the problem is an intake leak and it gets fixed after clearing the codes I would be curious if they come back.

For the O2 code check all the wiring of the sensors, perhaps something got damaged or disconnected and it is related to the high idle rpm and p0507, say perhaps the .airbox was removed and then one of the o2 sensor wires got pinched or something..

Edited April 14, 2012 by logray

[P2C4]

It does idle high.

I reset the above codes, and it struggled to idle low, at about 500. I helped it, with the gas peddle, idle a little above 700. Then it started idling at 1000, and then within 5 miles of city driving it was idling pleasantly at 1.5K. Then soon threw the CEL. I read the new codes: P0507 again, and P0410 Porsche Fault Code 80 - secondary air injection system (Cylinder 1-3).

I'll try your above suggestions, and report. Thanks.

Edited April 14, 2012 by P2C4

[P2C4]

Logray: I appreciate your help.

I didn't find any intake leak. Wiring looks healthy and happy.

How do I learn what the fuel trims are at??

Yes, throttle is egas on my car.

So, removed and cleaned the throttle body, and had my daughter with a smaller hand reach way back in to the left and right and wipe with a cleaner soaked rag, within the depths of the tube behind the throttle "butterfly" valve. It wasn't that dirty. Cleaned the mass air flow sensor again. Cleared all codes. No other codes came back except the 507 code, which would always light the CEL within 5 miles of city driving. No other codes in 400 miles. And it would fuss around at a low idle (600 ish), and then 1000, and then light the CEL and idle at 1400. That was the consistent patter every day last week after I re-set the codes.

So today I replaced the mass air flow sensor. And that helped a great deal.. It was the original MAS, and had 145K miles on it, which apparently is too many. CEL light has stayed off.

The idle does still seem a little high, at about 800. But it doesn't start out with a 600 dip in the idle. It just idles 800 and it seems from the tachometer to be a steady idle, but reading RPM with Durametric software shows fluctuations from about 810 to 825.

Isn't idle supposed to be steady at 700?

Any suggestions for why the idle doesn't lower?

[logray]

With a hot car in good working order, the idle should be about 680 RPM and very steady.

The most common cause of a higher than normal RPM is probably an intake leak. If you don't have a smoke machine or are comfortable using a propane probe, I would encourage you to hire some shop time to have the car checked out for intake leaks. Even a tiny leak from a very tiny vacuum hose could cause enough of a leak to cause issues. There are lots of those all over the engine, from FPR, to SAI, resonance flap, etc.

If you are CERTAIN there are no intake leaks or issues perhaps your fuel pressure regulator has failed?

It could also be a problem with idle air control valve (99 C2) or throttle body (later cars).

Lastly, on cable operated throttle body, (99 C2) if the cable is not routed correctly it can cause the flap to be slightly open at 0 degrees pedal.

[wvicary]

It sounds like a vacuum leak. As suggested have the system smoke tested with special attention paid to the EVAP system.