Yet another SAI question... RPM behavior

RL 996ers -- I am at a loss after speaking with a few knowledgeable friends, my mechanic, and extensive searching on RL, Planet 9, and other reputable tech forums. Last week, I changed my alternator, and in doing that, decided to unplug (no power) the SAI after getting the infamous buzz-saw sound on start-up. I was planning to address it as soon as I had the time, and did not want to cause any additional damage or wear. Prior to disabling the SAI, I spoke to a friend who was a former Porsche tech and consulted the forums/Bentley & Pelican DIY manuals, and it seemed there is no harm in disabling the system since it is solely for emissions control. After doing that the following occurred a few days later (17-19OCT): 1. Noticed an RPM dip coming to stop from ~700 (where the needle likes to hang) to low 600s (short trip to pick up a serpentine belt prior to a road trip, I always keep a backup and used that when I changed the alternator) 2. Following day - Cold start with cooler ambient temperature (42-45F), I start the car to make a short drive to the staging area for (funny enough) the Porsche Boardwalk Reunion (which was fantastic). On the drive over, I get the P0491 code (left bank). Parked the car, reviewed the code, cleared it since it is attributed to the SAI 3. Yesterday, coming back from New Jersey, I noticed another dip in the RPMs, same behavior sitting on the 495 parking lot outside of the DC area This RPM anomaly has only happened at idle and when making a short trip or sitting in traffic as mentioned twice above. I also understand the SAI can power up when coming off a freeway and/or long stretch of driving under load, so not sure if that has something to do with this weirdness. The car, in September, did trip the P0456 code (small evap leak), but after ensuring my gas cap was tightened, that has yet to return. My question, after seemingly stumping those I know in the area that I trust with good knowledge and wrenching skills, is there something more at play here that I should consider? I don't want to throw a new SAI at the car yet, and the plan is to remove the unit, clean it, grease it, get it back on and go from there. If I still get the screech, then I will replace the SAI. Could this be the car relearning after disabling the SAI? Maybe it's looking for a process/function that normally occurs, and in doing so, it is affecting the RPMs? Not sure how the 996 generation goes about remapping/learning when you disable something like the SAI... My ignorance. More importantly, I also want to ensure I am not missing something here or I misunderstood the affect the SAI would have on the engine. Last thing I want to do is cause more problems with bigger price tags. I have yet to smoke test the car, but that would be my first step. Other considerations: MAF sensor needs to be cleaned and/or reseated (I had if off to take the airbox out to do the work); I replaced the airbox filter with the Rennline filter ( https://www.pelicanparts.com/cgi-bin...cgi?pn=REN-M76 ) too and wonder if that's causing the issue...? Any thoughts are welcome, and while I know there is a ton out there, I can't seem to find anything prior which addresses this type of behavior after disabling the SAI. The car is a daily driver, and weekend auto-Xer, so I plan on getting the SAI back up and running regardless. Just thrown off with the aforementioned issues. Thanks to the RL 996 community. You guys are a great resource, and much appreciate any help.

I can concur the SAI can run after long drive at speed - after morning startup. I started the car, had light traffic and no stops on the way to work (35 miles). When I did get off the freeway, first stop light I got a check engine light. Checked codes - if was for SAI. I had accidently left it unplugged after some work the previous day. Easy fix. As to how to silence a noisy unit - have not had to do that yet. -Tom 2003 C2

U probably cracked the oil full tube installing the alt cause a crank case vacuum issue. Happens all the time.

Much thanks to both of you! I hopefully assume, if I did crack the oil filler tube, that replacing that should remedy the issue? *fingers crossed* Much thanks, and will take a look at it in the morning. Safe to drive the car or should I hold off until it's inspected/repaired (if damaged)?

I agree with dejeeper on the cracked filler connector. As to the SAI, I cleaned out the airfilter on it with compressed air and that helped, but the real problem was the air shut off valve. When the air shut off valve that controls the SAI input into the manifold fails, it fails in the closed position. The blower still comes on, but there is no place for the air to go. The check valve and air shut off valve are now one piece. Used to be two. I can get a part number tomorrow if you want.

That would be fantastic! Much thanks.

So the motor needs the correct amount of crank case vacuum for somethings to function like the aos. I would say u r fine for regular driving but avoid the track or aggressive drives. Some have been successful in repairing the tube with large electrical wire heat shrink or even rubber plumbing furnco connectors as a temp fix.

Quotes source post: 19706009

This part of for '00 and later. 99711324990 Here is the schematic M96.01/02/03 Air Injection M96.04 (autoatlanta.com)

So my idiot-self forgot to mention that I changed the oil after the alternator, and everything was fine. Filled it up, no leaks/drips, then topped it off the following day at the start of the morning with nothing prevalent and it's holding... Needless to say, I need to check and it could be on the top side of the tube.

Have you ever wondered how the car knows that the SAI is not working? It does a self-test regularly when the engine is running in a predictable condition. When the car is fully warmed up and running smoothly, the ECU will turn on the Secondary Air Pump to introduce extra air into the exhaust. It expects the O2 sensor to pick up the extra O2 in the signal path and detects a running lean condition. If those conditions are not met (more than once), the ECU throws up a Check Engine Light and an error code related to the SAI. Your unplugging the secondary air pump has caused the CEL and the error code.

Thanks for the feedback and assistance so far! Disassembled and rebuilt the SAI (everything looked as should), tested it, and the buzz-saw sound is near eliminated. However, when you push on the hose connected to the elbow that channels air in, you do hear a faint murmur of that awful sound. It is infinitely better than what was there, but I ordered the three bushings that mount the SAI to the bracket, and am going to take another look at the hose to see why that specific area, when pressure is applied, gives a faint screech. EDIT: now it seems to be intermittent, high pitched, then subsides, like at certain intervals there is metal contact or something is not functioning, and referencing earlier posts, maybe the air shutoff valve (S99711324990). Any way to actually test the valve on its own? Compressed air? Did a visual inspection of the oil filler pipe, and it appears well intact, and refitted the cap in the even it wasn't properly seated after changing the oil. Still have yet to get out and drive the car since I've been at work, but will report back if the (slightly) wonky RPM behavior is still there. Thanks again and any additional ideas or known solutions are welcome. Really appreciate it.

Still getting intermittent saw sounds. Blew the SAI out, disassembled with compressed air. Hell of a lot of carbon (or at least very fine dust) to include chunks. Going to apply some light lubricant, and reinstall. Fingers crossed.

Stop screwing with it and replace the damn thing....lol If you do a search there is a Mercedes SAI pump that is a direct replacement for LOTs less expense ... Search the threads for the part number ...it will save you loads of $$$ ..

I should have a quiet 3.4l mk1 pump in one of my bins that i am sure i could be talked i to letting it go. Pm f u want it.

We greased it and it's running well now. Screwing with it is how you learn right? I mean that's how half this community keeps their cars on the road with DIY.

Yes you will learn that greasing a rusty old failing bearing will quieten it down ( think miniature IMS bearings).....for a while.......If you really want to learn you will source new bearings and replace them....I just thought the hours you have spent and are going to spend, that your time was worth more and was trying to help with good advice....but you know what your time is worth more than I do ...

I agree that with a DIY mentality (screwing with it) is how one learns and the forum is at least 25% DIYers. For professional, and semi-professionals, whose times are billed by the hours, screwing with it costs something and someone has to pay for that. As for me, I have stopped screwing with it a long time ago. Replace with factory parts and go on with life. Spend more time with the grand kids and my wife.

Quotes source post: 19713631

Totally didn't intend to come off as snarky, and agree, when it does come back, depending on time, I will either replace the bearings or just get a new unit. Thanks again everyone! I have a pretty demanding job, crap commute, but if I can make the time, I will. To each their own

Quotes source post: 19714783

It's Sokay , it is just an SAI pump !!! .I have been on this Forum for over a decade, you have to have a fairly think skin....lol....I get really upset when I see people screwing around with something that can end up with catastrophic engine failure...