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OK, so ask yourself this, did the car have these problems before you worked on it? Yes, than it was an existing problem.
No? Then it was likely caused during the repair. Which means, you just need to go back and check everything. Did you check that
red rubber gasket on the oil catch/SC intake? You need to lube it up with a little oil and make sure it doesn't get smooshed when putting that piece
back on. All hose are connected and good?
Whooshing sound: You know that this car uses the SC as an air pump to help heat the Cat on startup, vs. electric motor in other cars, right?
If you didn't know, thats likely your whooshing sound. I'd check all the gasket and hoses.
As fas driving like a granny to get past smog...uh, so what if you drive harder CEL comes on?
So you're clearing it, and then driving easy to smog?
If you clear it, you also clear all the readiness indicators and you will fail.
I've written about this frustration quite a bit in the past.
Take it to where your school is and register it there. Do they have smog? Doubt it's as much as PIA as California.
The car had intermittent boost issues where the supercharger needed the recirculation valve reset before.
Now I get a CEL, P0243.
I'll try cleaning the MAF, replacing it, then replacing the recirc valve, but I do wanna get the coupe smogged.
The red gasket has been checked many times and lubed up very thoroughly, so I doubt it's the problem.
I'm assuming that when the engine is under a certain stressful load, the coupe gets a tad bit cranky and the CEL comes on.
But I have a plan.
I just let the recirc valve do no boost, then I can redline the car as much as I want and get no CELs and happily pass smog.
I need 200ish miles after clearing the codes, right?
The thing is, I'd need to smog the coupe before I can register it in AZ, which means I need to get it smogged anyway.
The coupe is a month-ish behind on reg, so I need to put on those miles fast.
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
Just throwing parts at the problem, well thats gonna get expensive.
Ask me how I know.
Did you have any of these codes before you took the head off?
If no, then something happened during head repair.
Does the Recirc valves move at all?
Is MAF throwing codes?
Before you do anything get a scanner that reads mercedes codes.
I just picked up Launch Creader Elite 2.0 for ~$125 to replace my
iCarsoft. I really like it. It cleared my SRS error where the iCarsoft would not
and has many more functions, many I would be scared to use,and don't plan to.
One thing I've always worried about if I was going to do this repair
was all the crunchy old wiring. You're gonna need apply your expensive education, put your engineer hat on, and
start checking voltages etc if necessary.
I'll tell you something I've been doing lately is using google Gemini.
If you ask the right questions it wll search the entirety of the internet for you,
and give you results it would take hours to find in second.
And you can keep refining those questions and wow it's really been helping me with this 'new' car.
A-holes at Walnut Creek Merc did not tell me about a transmission issue.
Saleman said everything was "perfect". Yes, cosmetically. Caveat Emptor.
Lastly you can get a pass to drive the car to Arizona. Do they require smog?
Last edited by C230 Sport Coup; May 31, 2025 at 05:21 PM.
No codes pre-head repair.
I'm leaning to the recirc valve kicking the bucket and the MAF needing a clean.
Ordered a new one on eBay along with the screen on the cluster.
The total came out to over $400, I'm gonna be broke.
I was thinking about getting that scanner, or a computer with Xentry on it.
If the wiring got damaged, I'm in for a hell of a problem.
I wish I had gotten to see you when you were in Walnut Creek.
At least you are making progress on the new coupey, I'm over here traveling while my coupe sits in her sad state.
Once I go back home, I'll spray some MAF cleaner onto the coupe, replace the recirc valve, and pray the CEL goes away and I can finally have boost again.
I tried, no luck.
How do you clean it so well that it snaps back into place really fast?
Mine sped up but was still super slow.
I pulled it apart and blasted out all the old grease with some rubbing alcohol then re greased it. Youll need to pull it apart enough to actually see the gears on the inside. The spring could also be worn out. Could try to find one at a junkyard as theyre pretty easy to take out.
I tried, no luck.
How do you clean it so well that it snaps back into place really fast?
Mine sped up but was still super slow.
You must remove the motor of the flap, it is bolted in with 2 torx. There is a bronze bearing at the bottom and a ball bearing below the gear. I cleaned and oiled them, that was the culprit in my flap.
Well horrible news.
The new Bosch recirc valve came in.
Replaced it and went on a test drive.
Warmed the car up, then it was redline 1st, redline 2nd.
Supercharger was screaming through 3rd, then at 4k I felt the boost turn off and the car go back into limp mode.
No CEL, so I thought I was off the hook for that.
Went to O Reilys to get some MAF cleaner since that could've also been the culprit.
Started her up and on the way back, again did the test.
Boost was back.
1st redline, 2nd redline, and then again at 3rd at 4k rpms boost cuts off and then sadly showed the same P0243 code.
I thought it was no issue, clean up the MAF and try again.
As I removed the MAF, I found that there was a decent amount of oil in the intake and on the MAF itself.
The car has smelled like it was burning a slight amount of oil, but I didn't think anything much of it.
My guess is my crappy attempt at making a PCV system failed and that let oil all the way into the intake, coating the MAF and MAP sensors giving an inaccurate reading and then throwing the car into limp mode.
I'll probably rip out the entire intake to clean and try to fix the PCV system.
Kinda sad about this, but luckily I caught it before it got any worse and I did some irreversible damage to my coupey.
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
If everything worked before you did all this, you must be overlooking something.
But as someone who spent a good portion of their life as tech type who fixed all sorts of problems,
in all sorts of hardware and software,
you never know it a part failed conindentally the same time as another repair,
or if you messed up on the reassemby somewhere. But typically the odds lean towards the latter.
And you also never know if a new part if good. I replaced my Recirc air valve TWICE (2nd was Bosch lifetime warranty).
It seemed to solve the problem for a while and then it came back.
But in the end, when I FINALLY got a good NOS Siemans MAF (most of the new one's out there suck)
and went through a couple Bremi's (garbage) and a bogus OEM one that failed immediately,
everything has worked perfect since then as far boost always being on. But any air or vacuum leaks will cause similar problems.
Oil in intake is quite normal, but you can try to clean the oil separator, it is a centrifugal type you must spray cleaner inside and spin the whole box (the box above the SC). The P0243 can be a secondary error because the ECU switched the flap off and not the cause of it.
On WOT the lambda is switched off and only the MAF is responsible. No idea besides the MAF.
Oil in intake is quite normal, but you can try to clean the oil separator, it is a centrifugal type you must spray cleaner inside and spin the whole box (the box above the SC). The P0243 can be a secondary error because the ECU switched the flap off and not the cause of it.
On WOT the lambda is switched off and only the MAF is responsible. No idea besides the MAF.
Been a while, got rlly sick and had rashes all over my body.
Couldn't even stand up and walk, let alone work on my car.
That sucked.
Here is how much oil I had in the MAF and intake right by the throttle body.
I don't think this is healthy, which leads me to believe something is really wrong.
The coupe has been sitting for a while and is now leaking oil.
I'll have to borrow some jacks and remove the full intake and try and find the source of this leak.
The oil in the MAF is kind of normal, you can clean the cyclone oil separator, helps a bit.
Tuning tip, remove the fine metal mesh in the MAF and the mesh below the TB (only the mesh, the ring is the gasket) ~ +5 HP MAF
Well, I figured out the P0243 code.
Reattached the PCV hoses that disconnected under pressure.
The cause of the PCV code was the SAI switchover valve, and after paying $70 for the superseded part number at a stealership, throwing it in the car resulted in me having full boost again!
The coupe sounds great, drives great, and is a blast.
But now a new CEL has shown itself.
P0101 - MAF not reading correctly.
I thought the cause was that I installed the MAF upside down (silly me)
So I cleaned it out and put it back in the correct orientation.
Then I took the coupe on a 2 hour long highway commute to get some miles on the car, and it performed brilliantly.
However, on the way back, the P0101 came back again.
The car still runs well, but I am stumped as to why I get the code.
I wonder if my MAF has given up, or if there is just too much oil on it.
I need to figure this out and pass emissions.
Well, I figured out the P0243 code.
Reattached the PCV hoses that disconnected under pressure.
The cause of the PCV code was the SAI switchover valve, and after paying $70 for the superseded part number at a stealership, throwing it in the car resulted in me having full boost again!
The coupe sounds great, drives great, and is a blast.
But now a new CEL has shown itself.
P0101 - MAF not reading correctly.
I thought the cause was that I installed the MAF upside down (silly me)
So I cleaned it out and put it back in the correct orientation.
Then I took the coupe on a 2 hour long highway commute to get some miles on the car, and it performed brilliantly.
However, on the way back, the P0101 came back again.
The car still runs well, but I am stumped as to why I get the code.
I wonder if my MAF has given up, or if there is just too much oil on it.
I need to figure this out and pass emissions.
i got a cheap ebay MAF and have the same p0101, you need a genuine siemens maf if you want the ecu to be happy. I have no performance issues with the ebay maf or cam pos sensor tho
There;s a low mileage one (a little over 100K) in Cinamon color which I hate for like 3 grand
But it appears from the photos that one side is cocked on the pano, and doesn't close. VERY bad.
The guy selling it is an ******* and won't speak to you directly or answer any questions! Just directs you back to his website,
Jerk! it's also a manual which I don't want. 722.6 tiptronic 5 speed is like the most awesome tranny every made. Change the fluid regularly and they never break.
And I don't want to have to deal with an eventual VERY expensive clutch repair. I'm done rowing the boat.
There also is a white one that just popped up as well they want a lot but it looks like heated electric seats.
There was a pretty nice silver one in Davis for 4 grand in cloth, sold.
There was a blue one in San Mateeo the guy wants like 6 grand and it's high mileage saying it will go
300K miles. Uh yeah naybe, not without some trouble. The paint looks faded, his ad was wierd,
I would only consider California car so many are in the south and Florida maybe in a flood and I've heard rust can be
a problem with so midwest is out these but mine has never seen snow or ice.
I saw a very low mileage C240 not cheap. Super nice but also super expensive I forget how much 7k maybe(?) and sedan.
Nah.
Yeah I would LOVE to find a car just like mine with a little above or below 100K miles, Orion blue,
FUNCTIONING sunroof, C7. etc. I can swap my goodies over. Buts it's a unicorn. So far it doesn't exist.
So I may swap engine with another lower mileage M111. I think at 260k doing head gasket and not chain doesn't make sense,
and then I'd still have an engine with 260K on it.
BTW- W209 CLK convertibles go all day long in really nice condition for cheap cheap cheap!! Same or less than C coupeys.
A car that sold for 60k is less or the same. S class too!
Nuts!
20000kms of abuse later still going strong; i thought the same since doing a head gasket job and ended up refurbishing the head (valve stem seals, porting, 5 angle valve job and valve lapping, rebuilt lifters).
I got a cheap 40usd chinese copy of the mercedes chain rivet/breaking tool (which is pretty much the only way to change the chain) and to my surprise i had 0 issues and i didnt have to use the tool for more than 10 minutes.
WRT timing it was pretty much set at factory specs with the new chain iirc 20deg intake 30 exhaust and i used lukas' youtube guide on checking the timing at TDC instead of WIS 20deg procedure.
This made a *phenomenal difference* in every which way the car behaves, it really woke up and didnt seem like it had 300000kms (yes 300) at all. Timing chain brought back a lot of top end power and i never heard a single rattle at startup since especially after rebuilding and cleaning the lifters even with 30 weight oil. Why i went through the trouble is i didnt have to hunt for a m111, drop an engine and put another in, the engine stayed in the car and 3 days, some beers and a damn good few hundred doll hairs saved and it ran like new so no reason to throw away these really strong engines bottom and top end wise. cant say the same for m271s tho lol
i got a cheap ebay MAF and have the same p0101, you need a genuine siemens maf if you want the ecu to be happy. I have no performance issues with the ebay maf or cam pos sensor tho
I picked up this MAF from the stealership and paid WELL over what it's worth.
Just dunno what to do now, I either think its the intake oil separator thats given up or another vacuum leak.
Either way, can't do anything right now as I am at university without the coupe.
I'm thinking of taking it to a shop and having them diagnose and potentially fix it since I am kinda just fed up.
Yeah it's not the cars fault, its mine but y'know, after doing the head gasket and having boost back I just want the car to be legal again and be able to survive the 1000 mile roadtrips I want to take her on.
I picked up this MAF from the stealership and paid WELL over what it's worth.
Just dunno what to do now, I either think its the intake oil separator thats given up or another vacuum leak.
Either way, can't do anything right now as I am at university without the coupe.
I'm thinking of taking it to a shop and having them diagnose and potentially fix it since I am kinda just fed up.
Yeah it's not the cars fault, its mine but y'know, after doing the head gasket and having boost back I just want the car to be legal again and be able to survive the 1000 mile roadtrips I want to take her on.
Hey on the bright side at least that car isn't the one you're relying on to get you to and from classes and back home (situation I'm in). Each time I get somewhere without any weird noises I give thanks. Have you thought about a potential engine swap? It sounds crazy but if the repair prices you're looking at cost as much as getting a new engine for it then it might be worth because you're able to have it not running for extended periods. Or maybe putting in a standalone ECU to rid yourself of all the Mercedes nonsense (not sure if that'll pass inspections in your state)
Hey on the bright side at least that car isn't the one you're relying on to get you to and from classes and back home (situation I'm in). Each time I get somewhere without any weird noises I give thanks. Have you thought about a potential engine swap? It sounds crazy but if the repair prices you're looking at cost as much as getting a new engine for it then it might be worth because you're able to have it not running for extended periods. Or maybe putting in a standalone ECU to rid yourself of all the Mercedes nonsense (not sure if that'll pass inspections in your state)
True, that is a plus.
Although I would kinda like it to be with me lol.
I feel like finding another M111K EVO would be impossible, and swapping to a M112 or M113 is not very economical considering I'd have to swap in a new transmission.
Standalone would probably cause some bs reason to not pass CA smog test.
I do think the P0101 is some wiring issue or a vacuum leak somewhere hopefully.
I do think a shop diag is worth it atp and would save me the headache.
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
Yeah at this point. Find a good shop who will actually do a dianosis and not just sell you parts.
Definately NOT Walnut Creek Mercedes. So "your car’s computer sees a mismatch between the amount of air entering the engine and the reading it’s receiving from the mass airflow sensor. This kind of mismatch can set a P0101,"
Just wondering...is the O rong in the plastic pipe where the MAF connects to the oupuut of the superharger still there?
A dealer lost mine once and it was years before I could find another as you can't purchase from Mercedes and
it only comes with the plastic intake pipe for $$$$. I got some Orings locally but they weren't exactly the right size and I had to jury rig with duct tape. Arrgh. I finally got one from a junkyard,
Is there air leaking out around the MAF? Any of the connections between the MAF and throttle body leaking at all?
There's a screen nelow the throttle body with a gasket is that still there?
What scanner are you using to read this error? P0101 is a generic error.
If you were getting the Mercedes codes you might find it.
After all how the heck does the car know there's a mismatch on air levels when the only
thing that measures that is the MAF?
Vacuum leaks resulted in lean conditoin for me. Not
P0101. Never had that one.
Last edited by C230 Sport Coup; Oct 25, 2025 at 09:51 PM.
If you have compressed air you can do an easy and fast vacuum test. Use the hose connector at the TB from the EVAP system for compressed air input, remove the air filter and close the oval inlet with a latex glove and a rubber band. Put pressure at the system and watch the glove get inflated and more important how slow it deflates. Should be very slow.
Yeah at this point. Find a good shop who will actually do a dianosis and not just sell you parts.
Definately NOT Walnut Creek Mercedes. So "your car’s computer sees a mismatch between the amount of air entering the engine and the reading it’s receiving from the mass airflow sensor. This kind of mismatch can set a P0101,"
Just wondering...is the O rong in the plastic pipe where the MAF connects to the oupuut of the superharger still there?
A dealer lost mine once and it was years before I could find another as you can't purchase from Mercedes and
it only comes with the plastic intake pipe for $$$$. I got some Orings locally but they weren't exactly the right size and I had to jury rig with duct tape. Arrgh. I finally got one from a junkyard,
Is there air leaking out around the MAF? Any of the connections between the MAF and throttle body leaking at all?
There's a screen nelow the throttle body with a gasket is that still there?
What scanner are you using to read this error? P0101 is a generic error.
If you were getting the Mercedes codes you might find it.
After all how the heck does the car know there's a mismatch on air levels when the only
thing that measures that is the MAF?
Vacuum leaks resulted in lean conditoin for me. Not
P0101. Never had that one.
When I return in December, I'll check to see if the O-ring is still there.
The screen below the TB is there with its gasket, but I'll double-check.
I am using a cheap FIXD scanner I bought a while back.
Along with the P0101, I sometimes experience a lean condition, so I think there may be a correlation.
I think the MAF connection is either wack or there is just too much oil being thrown at it.
Maybe my oil air separator failed. I'll probably tinker with the coupe some more when I go back home, and hopefully, by Christmas, she will be legal again.
If you have compressed air you can do an easy and fast vacuum test. Use the hose connector at the TB from the EVAP system for compressed air input, remove the air filter and close the oval inlet with a latex glove and a rubber band. Put pressure at the system and watch the glove get inflated and more important how slow it deflates. Should be very slow.
I will try this as well, thank you!
I wonder if all my fiddling with the head gasket has messed up some of the hoses, and that's why I'm having these problems.
If I have to go deep into the motor again, I will be bummed.
I just want to have fun with this coupe after all that effort.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
Caveat Emptor.
