Mass Air Flow Fault Problem - Ideas???

[tjim01]

Hello All - First post in this group, looking for some suggestions...

 

I picked up a used 2013 Cayenne GTS with an engine light on and running poorly.  Took to a Porsche dealer who replaced the throttle body, ECM and high pressure fuel pump, which fixed nothing. I then took it to a well known local German car specialist, who quickly diagnosed it with extremely high crankcase pressure, replaced the crankcase breather, which fixed the running poorly issue.  However, it still threw a MAF related code (P1074 and/or P0068).  They replaced the MAP sensor, but it didn't fix the issue (so they removed it and didn't charge me for the part, like Porsche!).  

 

The puzzle is this - they said the MAF code is thrown based on the combined inputs from the throttle body, ECM and MAP, but as the 2 of those are new, and one (MAP) is confirmed not to be the issue, they don't know what else it could be (all related wiring was checked by both Porsche and local place).  I'm still in contact with Porsche mechanic and he suggests it "could" be caused by one or more bad/stuck valves in the intake....makes sense to me, but as I've poured quite a bit into issue already, I thought I would try to get more opinions. 

 

What's your thoughts and thanks in advance...this has been much more trying than expected, to say the least.

 

Jim 

[deilenberger]

If he means intake valves to a cylinder - that would be rather obvious with rough running and lots of error codes besides an MAF code.  They replaced the "MAP" (Manifold Absolute Pressure sensor) - have they replaced the MAF (Mass Air Flow sensor)?  Is there one of each on the '13 GTS?  (Dunno, I have a turbo, and there is no MAF, just the MAP sensor..)

[tjim01]

10 hours ago, deilenberger said:

If he means intake valves to a cylinder - that would be rather obvious with rough running and lots of error codes besides an MAF code.  They replaced the "MAP" (Manifold Absolute Pressure sensor) - have they replaced the MAF (Mass Air Flow sensor)?  Is there one of each on the '13 GTS?  (Dunno, I have a turbo, and there is no MAF, just the MAP sensor..)

Thank you for the reply Don - The valves the mechanic is referring to are in the runners of the intake.  There is no "MAF" sensor.  I am told MAF is based on the combination of the 3 inputs (ECM, Throttle body & MAP) as mentioned above. The intake itself is the only other element I believe left to replace, which seems to make sense and have any thing to do with this....but I've said that many times already, lol.

 

In addition, after putting a few miles on it after picking it up, it still runs poorly even after the crankcase breather, most noticeably under no/light load - as if the "choke" wasn't working correctly.  Very "jerky", falling on it's face then hard acceleration...like a poorly adjusted old carbureted vehicle.

 

Please share your thoughts...about to drop $600 on an intake and take another shot...

[deilenberger]

Intake Manifold.. appears to be the same for all normally aspirated V8's - and I didn't know of any valving in the intakes. So - I went poking around the web, and apparently there is some device used for some function on the intake manifold of normally-aspirated 4.8L V8 engines:  https://www.pelicanparts.com/catalog/SuperCat/958C/POR_958C_FULINT_pg2.htm  (I found several other references to it - but no explanation of what it does or how it fits into things..)  So I poked around on the factory service manual, and found a reference to it. It mounts on the back of the manifold.  Purpose unknown, but it might be to add length to the intake runners based on ?  

 

I'll try attaching a screen-capture.. 

 

 

 

Since you can buy that as a separate part - it might be more economical than buying an entire intake manifold. I think the first thing I'd be looking at is the two hoses. It would appear #1 might well be a vacuum hose since the round part on #6 looks a lot like a vacuum actuator.  And that seems to be moving the rod #9 that connects to the two bell-cranks (#5 & #8) that look as if they might turn something in the manifold - like maybe some butterfly valving to change intake lengths.

 

FWIW - the turbo doesn't seem to have any of this - I would guess because it just pushes air under pressure through the intake, rather than relying on engine vacuum to pull the air through.

Edited October 11, 2018 by deilenberger

[tjim01]

Thanks Don! I believe the vacuum control you show could possibly be the issue.  I can't however find anywhere any vacuum specs to test it with a Mighty-Vac.  If anyone can find something, I'm all ears...  I may also call Porsche and see if they can provide something.  I also may pull the intake and stick an endoscope down each runner to see these valves look like...maybe one somehow got bent or is obstructed...long shot, but curious now just to see inside, lol.

 

BTW - Search this video on youtube for a good simple explanation of the function of these valves...."Variable Intake Manifolds & Intake Tuning"

 

 

Edited October 18, 2018 by tjim01
Removed wrong video link (advertisement)

[Dan.Magherusan]

Had this issue when I bought mine (used) and it turned out that the guy that had previously worked on the car forgot to plug it back in...

It's a slim chance you have the same problem, but it's worth checking...

Sent from my SM-G950F using Tapatalk

[tjim01]

OK guys - I'm still chasing my problem.  I did replace the entire intake with a new one.  I removed and inspected the old one and the actuation on the runner valves seemed a bit "sticky" to me, but it did not help.  I did run an endoscope down the runners and actually have a video of the valves operating, if anyone was interested to see whats going on inside these things.  I also bought an icarscan code reader to continue the pursuit and this is where my next question comes in....

 

I get the following codes: P0068 "Mass air flow implausible" (limit exceeded), P1074 "Mass airflow partial load implausibly high" (below exceeded) and P0660 "Intake manifold switchover driver" (No signal/communication).  From a previous post I stated the MAP sensor was already tried and that was OK.  I realize it still could be a bad ground or vacuum switch/leak somewhere...but here's the rub - it runs rough when the code gets thrown, but as soon as I reset the code, it runs perfect again.  If something mechanical was bad, how could that be?  It's like the code itself is causing the problem - just not sure was causing the code...what's your thoughts?

 

Also, is there a suggestion of another forum or place to ask this question?  Would like to get as many thoughts as possible....

 

Thank you!

[deilenberger]

The manifold pressure sensor is a WAY cheap part if you search on the Bosch number that's on it. It's used on everything including Chebby's.. you should find more auto parts stores stock it. I'd try a new one and reset the fault code again.

 

As far as another forum - I might suggest rennlist.com - it has an active Cayenne forum (I moderate there..)

Edited December 8, 2018 by deilenberger

[tjim01]

Will do sir - was thinking the same, even though the shop said it did nothing when they replaced it, I kinda wished they would have just left it on - thanks for the input.

[F SANE IL]

Hey, I know I'm 4 years late to the conversation. Was this ever resolved?