Weird stalling problem

[geoff]

Original owner 2005 997 Carrera Tip, 191K miles, my wife's daily driver. Engine replaced by Porsche in 2011 around 60K miles when IMS bearing let loose. Lately in the morning on cold start, the car stalls at the end of the driveway first thing in the morning with the headlights on. Then runs OK, or sometimes stalls one more time in the next block. Doesn't stall when the headlights are on, but stumbles once or twice in the first few minutes of driving in the morning, then all is fine. Took to the dealer (never had any complaints), and the tech cleaned the throttle body. Check engine light came on by the time I got it home and the car continued to stall in the mornings. I'm in So Cal, so cold start is in the 50s outside temperature. Codes are P2189 and P2187, which indicates the engine's air-fuel mixture is too lean on bank 2 and bank 1 while idling. Tech then said found broken line for brake booster and replaced. Check engine light still on. Car still stalls. I then replaced the 9 year old Optima with a new AGM battery, but that didn't solve the problem. Back at the dealer this morning. Service advisor is now telling me the techs think it's a bad AOS, even though the car isn't smoking. Story is coming from 3 techs, including shop foreman. Their diagnosis was based on oil cap is hard to remove, and "oil filler neck is sucking in". I asked for what pressure measurement they got for crankcase vacuum, but didn't get a straight answer.

 

Before I spend $4K to replace the AOS, which doesn't seem to me that it's the cause of the problem because there's no smoke on startup, what else should I have them look at?

[Loren]

P2189 Lambda control adaptation FRAU (lower load range) (FRAU > 0.7)
- below limit value

 

Possible fault causes

- Incorrect main filling signal from hot-film mass air flow meter

- Fuel pressure too high
- Injection valve faulty (dripping)
- Tank vent faulty (does not close completely)

 

P2189 Lambda control adaptation FRAU (lower load range) (FRAU > 1.3)
- above limit value

 

Possible fault causes
- Intake system leaking (secondary air)
- Incorrect main filling signal from hot-film mass air flow meter

- Leak in exhaust system

- Fuel pressure too low
- Fuel injector faulty (stuck)
- Fuel pump delivery too low

 

 

P2187 Lambda control adaptation FRAU (lower load range) (FRAU > 0.7)
- below limit value

 

Possible fault causes
- Incorrect main filling signal from hot-film mass air flow meter
- Fuel pressure too high
- Injection valve faulty (dripping)
- Tank vent faulty (does not close completely)

 

P2187 Lambda control adaptation FRAU (lower load range) (FRAU > 1.3)
- below limit value

 

Possible fault causes
- Intake system leaking (secondary air)
- Incorrect main filling signal from hot-film mass air flow meter
- Leak in exhaust system
- Fuel pressure too low
- Fuel injector faulty (stuck)
- Fuel pump delivery too low

[geoff]

Thanks Loren, as always!

 

None of these are sounding like they are caused by the  AOS going bad, are they? I'm going to visit the dealer to see what's going on tomorrow.  From the way my wife has described the symptoms, it seems like it would be a fuel or electrical issue causing the car to sputter and/or die. The CEL didn't start until after the first visit where the tech cleaned the throttle body. Before that, it was idling smoothly, just stalling. I'll see if I can get more details.  Anything else this could likely be?

[Loren]

See if any of the fault codes have changed. If not, then I would still go the path based on the FRAU readings.

[JFP in PA]

The AOS can either be pin pointed or eliminated by having the car's sump vacuum level checked with a digital manometer (most quality shops have them as the AOS is a perpetual issue; surprise the dealer didn't do this).

[geoff]

I asked my service advisor last night for specific measurements, but all I got back from him was "Oil cap hard to remove", which in all fairness is his level of mechanical expertise and understanding (he came from Porsche sales and doesn't know much about how the cars actually function in terms of problems, and the techs know this, but he does go out of his way not to sell unneeded work). I don't doubt the AOS is starting to fail after 14 years and around 150K miles (no visible symptoms yet), but more worried that replacing the AOS won't solve the cold start stalling problem (only stalls after initial cold start in the morning with the headlights on, but never after that). I'm going to the dealership to talk to the techs and get the details firsthand, and will report back what they say.

 

And it's not like I don't spend enough at the dealer that they need to make more money off of me. I went deer hunting on a canyon road at 60 MPH, and instead of filing a comprehensive claim with my insurance for my '08 Cayenne, I'm having the dealer fix everything, including subletting all the body work.

[JFP in PA]

If the oil cap is hard to remove, you have a high vacuum level in the sump, which is bad for a variety of reasons, including lean stalling.  The correct way to access the AOS is to fully warm up the engine by driving the car for 10-15 min, then replace the oil cap with the one in the picture above with a hose that connects to the digital manometer.  If the vacuum level exceeds 6-7 inches of water vacuum, the AOS is leaking air into the intake system, causing the lean stall conditions.  The normal level of vacuum is typically 4-5 inches of water, which is a really weak vacuum level, so it doesn't take much of a leak to cause problems, which is why we always checked every car that passed thru the shop with the manometer.