When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
A little background to start. I've owned a Boxster S and Cayenne S in the past, but I'm new to 911 ownership. I'm always up to DIY the easy stuff (oil, brakes, stuff like that), but I'm certainly no mechanic).
I recently purchased a 2009 Targa 4 (997.2 3.6). It had very high miles (95k then, 100k now), but the price was right and the engines seemed to have so far proven reliable so why not, right? I'm anticipating the issues that come along with owning a high mileage car and the first one has recently arrived.
I'm dealing with a flashing CEL and misfires on all cylinders 4,5,6 (all of bank 2). I've been told to check everything from MAF to plugs and coils, to AOS and variocam system. Anyway, I won't go too far into the troubleshooting except to say that although I'm totally averse to replacing good parts for no reason, I've noticed that lazy dealerships and mechanics seem to be doing that more and more. So rather than handing them hundreds and hundreds of dollars to troubleshoot and throw parts at it, I decided to do the easy stuff my self.
Found oil in intake plenum (small pools) and oil coating the throttle body. I was never convinced the AOS was causing my misfires because they were isolated to just one bank and the AOS affects both banks equally. But I was getting some indications the AOS was starting to fail and my Porsche mechanic said that's where'd he'd start if I brought the car to him. Part was $100 even from the dealership and book time was 3 hours, so I decided to change it myself and save a little labor cost.
As stated earlier, I am not a mechanic and have zero expertise on the subject. But I couldn't find a thread anywhere showing how to replace an AOS on the 997.2 motor. As a matter of fact, it took me 5 minutes and a flashlight to even locate the sucker. Since my car has more miles than most others, I thought I'd throw something on here in case it helps anyway. Take it with a grain of salt!
Now to the Job:
1. Start by removing the air filter housing (disconnect MAF sensor electrical connector, remove claps connecting it to the throttle body).
2. Next to come off is the throttle body (disconnect electrical connector and 4 torx bolts).
3. Now you need to remove the intake plenum (at least I think that's what it's called) forward of the throttle body (pop a couple quick disconnect air lines and metal clamps, slide rubber boots out of the way).
(I didn't take pics of the above parts' removal because I only decided to document the install at about this point)
Now you can see the AOS in the forward passenger corner of the engine compartment. It's pretty simple to get out at this point. 1. Follow the quick disconnect air line you already removed from the intake plenum and disconnect from the top RH side of the AOS. 2. Remove the two torx mounting bolts (a swivel connection on your ratchet makes it easier). 3. At this point, the AOS is only held in place by the two outlet ducts on the bottom. Just wiggle and pull up and it will come out. Mine was pretty tight. I had to pry a little bit with a flathead screw driver.
Back in is obviously the opposite. I ran into a couple problems though.
1. With new o-rings on the two ducts on the bottom of the AOS, it's a very tight fit back into it's manifold and it's difficult to get any leverage to push it down. I spend about 10 minutes trying to seat it with no luck. Then I had the bright idea that if I just lined up the AOS and slowly tightened both mounting bolts, the o-rings would seat into the manifold. DIDN'T HAPPEN. The mounting bolts went all the way in and tight, but the AOS was still sitting about 1/4 inch high (See picture).
Removed mounting bolts and spent 30 min or so building a makeshift pry-bar to press that AOS into place. Pain in the ***, but it finally seated properly. Replaced mounting bolts and air hose to Intake Plenum. I used a flashlight and inspection mirror to check that it was properly seated (See picture).
Replaced Intake Plenum. The boots and clamps are kind of a pain in the ***. Inspection mirror helped here too to see the back. While attempting to reconnect its hoses, I realized I had trapped one of them under the plenum so I had to remove it again to reposition the hose. Rookie mistake. Got it all sorted.
Replaced Throttle Body and Air Filter Housing.
Done deal. Shop time by Porsche was 3 hours and with all my drama, it took about 3 hours. I could easily do it a second time in about 1 hour so you guys can probably do it the first time in 45 minutes. I even spend 15 min jacking up the rear of the car, just to go look underneath and realize there are no clamps or anything down there. No need to be under there for AOS.
Turns out there was probably noting wrong with the AOS in my car. I took it apart and inspected the rubber seal which I believe is pretty much the only part that fails. It looked fine. Had I any confidence in my knowlege about the AOS operation, I probably would have just put my old one back in and returned the new one to Porsche. But what do I know? Maybe it is bad.
Supposedly there are several ways to test a failing AOS (lots of smoke from tailpipe, large vacuum suction from oil fill tube, oil pooling in intake plenum, squealing sound kind of like a belt).
My symptoms were only a small amount of oil in intake. Turns out that's normal. I also get a squealing sound sometimes. That turned out to actually be the belt. Oh well. Don't have to worry about my AOS for a while, hopefully.
1. Would it be good procedure to apply a bit of motor oil to the seals? This may help them slide in easier no?
2. Describe "pools of oil" that sounds a bit scary to me
3. I cleaned my throttle body but I did not remove the body itself. I sprayed some cleaner on a rag and got in there as I could with a rag. The thing was BLACK inside but no pooling or anything wet. What was the inside of your throttle body like when you removed it?
Peace,
Bruce in Philly
Last edited by Bruce In Philly; 10-27-2015 at 10:24 AM.
That doesn't seem that arduous compared to the 996. I think the 997.1S is in a different position than the 996. I wonder if it is as easy as this one to replace?
Nope. On the 997s, the AOS is tucked way in the back of the engine, towards the firewall/bulkhead, like the 996.
Need to pull out the driver side manifold to get to it, which looks like a royal PITA. I want to upgrade to the Cup car AOS, but I just don't have the time to open up and manage that can of worms.
If I was going to spend all that time and knuckle scraping I would have upgraded to the Motorsport Version. Good for you for getting in there.
That's how new I am to the car. I didn't know there was a different version. I have to say though. My car has 100k miles and the AOS I took out looked just fine. Diaphragm felt strong, but then again, I don't have all maintenance history for my car. It may have been replaced. I have no way of knowing. I asked the parts guy at Porsche in Rocklin, CA if he'd order many and he said he couldn't remember ordering an AOS in quite a while. Maybe they're a solid part this go round.
1. Would it be good procedure to apply a bit of motor oil to the seals? This may help them slide in easier no?
2. Describe "pools of oil" that sounds a bit scary to me
3. I cleaned my throttle body but I did not remove the body itself. I sprayed some cleaner on a rag and got in there as I could with a rag. The thing was BLACK inside but no pooling or anything wet. What was the inside of your throttle body like when you removed it?
Peace,
Bruce in Philly
Bruce, I wasn't sure what to lube the o-rings with so I did a quick search and read somewhere that motor oil wasn't the greatest thing to use and that some manufacturers recommended vegetable oil. Since I had that handy, that's what I used.
My throttle body was fairly clean on the air filter housing side, but had a good amount of carbon build up and oil on the intake plenum (forward) side. Took some scrubbing with throttle body cleaner and a soft bristled brush to make it shine again. But to be honest, I don't think being a little dirty effects them much. It's probably not until they get so carbon crusty that they stick open too much or can't operate smoothly. I saw no indication of that. But once you get the air cleaner out, you're only 4 quick bolts and an electrical connector away from having the whole TB off so you can clean it. Very easy job. Just don't break a perfectly good part while trying to tidy it up a bit. That's always my fear when tinkering.
I would say all the exess oil I wiped up from inside the intake plenum and each intake manifold probably made up about 1 tsp. I had initially thought that ANY oil in the air intake system was abnormal, but after reading more and more, I realize a small amount is normal. I say "pool" only to differentiate what I saw from a light coating because there was a little more than that sitting on the bottom, but very little. My guess is that if you don't have continuous visible smoke from tailpipes, there's not too much oil in the intake. But I'm no expert.
Nope. On the 997s, the AOS is tucked way in the back of the engine, towards the firewall/bulkhead, like the 996.
Need to pull out the driver side manifold to get to it, which looks like a royal PITA. I want to upgrade to the Cup car AOS, but I just don't have the time to open up and manage that can of worms.
Carmichael, I think you are thinking of the 3.6 motor. I have the 3.8 S, the AOS is on the passenger side of the engine. I am not sure how easy it is to access though.
Awesome write up! Thank you Craig! (btw Hello from San Jose, CA )
I just got my 09 carrera, the AOS is leaking oil a bit, functionally, everything is fine, if not perfect.
I got a quote for 900$ to replace it.......
Your write up is so clear that I'm kind of confident now to do it myself
I just did this on a 987.2 and what a PIA it was. I'd rather do a 996/986 AOS over these. Just my opinion. This is a great write up! Thank you for that
Awesome write up! Thank you Craig! (btw Hello from San Jose, CA )
I just got my 09 carrera, the AOS is leaking oil a bit, functionally, everything is fine, if not perfect.
I got a quote for 900$ to replace it.......
Your write up is so clear that I'm kind of confident now to do it myself
nulee; I've done this DIY recently as well and will add a few more pics with some other pointers ASAP. You just need to be patient, especially when remounting the air distributor tube. It's one of those DIY's that will always be a lot easier the 2nd time around.
if you have a chance to measure the vacuum level before and after AOS replacement, and add your data to this thread below, it would be a helpful comparison for all of us.
10-27-2015, 12:44 AM
Replacing 997.2 Air Oil Separator AOS
