987.2 2.9L AOS Manometer readings

I have searched here and the Internet for the correct readings to test the AOS on my 987.2 2.9L. 15k miles ago the dealer diagnosed it failed, replacing the AOS but did not replace the hoses. All I found was inH20 for a 987.1 which is between 4-6. My readings are 19.5 when the vehicle is warm (22.5 when cold). I think the MA1 engines are 15-17inH20 but that could be wrong. Can anyone confirm what the specs should be for my engine and are they the same as all MA1 engines? I occasionally smoke at startup, maybe every 6 months or so. But my idle is lumpy, I replaced plugs and it made no difference. I'm about to replace coil packs, but I don't suspect I'll see an improvement. No significant oil burning to where the dipstick level changes. There is an oil burning smell after every warmup. 44k miles, 2010. I need to get this sorted in the next two weeks before a road trip. I am assuming the pipes could crack if I start removing them and testing them individually for leaks.

I don't know if there is a true spec anywhere, but I believe 15-17 is correct from what I remember. It's definitely higher than the 987.1 , because the AOS is different in design. I'd say your reading seems fine. As for the lumpy idle, you did plugs but not coils - generally you want to do them at the same time. You may see an improvement with that, as they do crack and have issues. I would think that 44k wouldn't be that old for this issue, but it's not out of the question. Bottom line, I think your AOS is fine. The lumpy idle should be addressed if possible, but I don't think either is really a problem for a road trip... assuming the car is fine otherwise.

Thank you for the reply and I really appreciate your opinion. With the 987.1 anything over 6 is out of range, if it's 7 or 8 it's really far gone. I looked back at the recording and it was 19.99-20.25 after the vehicle had been fully warmed up and driven hard for over 30 mins. Wouldn't it seem that +3inh20 out of range would be pretty far off from fine or are you looking at this from a percentage point? I just assumed that if it's within range it's fine, out of range it's bad.

Damnit, I think you may be right. I thought the vacuum would get worse (lower vac readings) when there was a problem, but it's the other way around (at least on 987.1 )... so you may have an issue, indeed. HOWEVER, if you had a cracked hose, then I would expect the vacuum level to DECREASE because air gets into the line... isn't that true? In other words, if a hose was cracked, you couldn't get BETTER vacuum levels... right? Maybe you should ignore me and see if anyone else chimes in with more experience... sorry for the confusion with my lack of detailed info!

I didn't replace the coil packs because it's a waste of $300 if the plugs solved the issues, i had an extra set of OE plugs and it's an hour to swap in new coils packs assuming the plugs were not the issues, no big deal IMO. I decided to pop the engine cover off and I figured I'd take a look at the AOS hoses. The top tubes that wrap around the intake ( before the intake manifolds) felt loose and there was evidence of grime around it. I took them both off and I found a black rubber seal which was broken on one end. I'll check the rest of them, clean up what little grime there is around the intake manifold and see if there's any improvement in a few months.

It's quite alright as I don't have a full understanding of how a Manometer works and I hear what your saying about the pressure as that seems logical at first glance. I know how to use one and read it, but without knowing a range it's all a guess. I'll check all the seals and replace what's needed and recheck the readings to see if it made any difference. If it doesn't I could just start replacing the hoses and finally the AOS . The hoses look ok to me and I don't see any visible cracks but it's corrugated so it's nearly impossible to visualize a small leak. There has to be pressure ( i.e Load) to test the hoses. Its not listed in my service manual but I feel like mine is incomplete. I am curious how Porsche service techs diagnose the AOS system?

With a digital manometer, for a healthy AOS the reading should be less than 6" of water with the engine at operating temperature. Edit: According to JFP on the 986 forum a healthy AOS should read between 4-5" of water..

I'm not sure that's correct for the 987.2 ... it is for the older AOS on the 987.1 and maybe the 986 , but the numbers are certainly different for later models... based on everything I have read.

I just found this by searching through google using slightly different keywords, "9A1 AOS readings" and found a thread "how to test your AOS " from another forum which you're probably all aware of. I can't post the link from there, the site seems to be a four letter word on Planet 9. I suppose this is as good of an answer as I can get, my readings are way higher. "MA1 Nominal crankcase vacuum is -15.0” (-14.0” to -16.0”) of H2O (not HG)." I reached out to Ultimate AOS because I was hoping their kit would work, they responded saying its not compatible and that they thought the readings were somewhere between 15 to 17 inh2O. FWIW, I've already paid the dealer $1400 4 years/9k miles ago. I change my own oil and fill it to 3/4 ( 1 empty box below the top arrow). A few months ago I had a 1/2 quart of fresh oil and needed the container to dump used oil. I decided to fill it to the top box, right below the arrow. Please correct me if I'm wrong, but I believe this to be considered a safe zone. It did smoke at a cold start within that timeframe so it's possible my dipstick reading is inaccurate or the max is truly 3/4 full. Either way I probably damaged the AOS 🤷🏼.