65fastback

So... slowly over the last couple months my idle has gotten pretty bad, once the car is warmed up in natural it moves up and down, won't hold steady, if i hit the throttle it will hang up at 1100 ish and drop down to 850 ish then back up ect ect..... No CEL or other issues the car pulls hard.
Had a shop that i work with put their star scanner on it and it showed 'purge valve detects minor vacuum leak"
I replaced the purge valve and no change.
Just bought a blue driver OBD ... it showed no codes... any help would be appreciated.

m a x i m u s

Sounds like a vacuum leak. Maybe the PCV? Did you do any mods or work on the engine lately?

65fastback

all I've done to it is change the oil and plugs. its stock no tune no exhaust mods, however i did notice someone had removed carbon filters before i got the car.

m a x i m u s

Maybe the air boxes aren't seated properly or became loose?

Mort

My theory is that the ecu scaling for the MAF sensors is overly sensitive in the 2009 MY. Removing the carbon filters causes the ECU to sense a lean condition and try to adjust for it but it fails. Your best bet is to try to reinstall the OEM air filters and carbon filters and see how it goes. This has been the remedy for a lot of '09 C63s. It is possible you do have a small vacuum leak. Get a good shop to test for a leak around the intake manifold and the PCV fittings as mentioned. It is also important to ensure the filters are properly installed and the box tops properly fastened down and the filter boxes are properly inserted into the intake horns and the clamps tightened down as mentioned. If you have access to OEM filters and carbon filters then reinstalling them is the easiest option and probably what you should try first.

Cli63

Could try and clean your MAFs, worth a shot since it is an easy job. Did it yesterday myself, took about 20 mins in total. Just make sure you are using specified MAF cleaners and not anything else. Good thing to note with a bluedriver, you could pull up a lot of values (MAF/MAP/engine load/intake temp.....) its a really helpful feature when you are trouble shooting.

Petakii63

Most likely the boxes are seated improperly. Has nothing to with carbon filters. These cars are very sensitive and will throw codes or CEL immediately if something is wrong. First things first is go get the latest software update from your Benz dealer. Secondly, put some new fresh paper filters in the boxes. And, some techron deep clean fuel treatment. Last but not least have someone look at the motor and tranny mounts. Those could also be the culprit.

65fastback

Great info guys! very cool... had the car up on a rack and motor & trans mounts look good.i'll try the above suggestions first, as far as using the blue driver i ran it for the first time yesterday, seems like lots of great "live" values and info... the trick is knowing what to do with the info.
It has Evap,system vapor pressure value... anyone know what this should be at idle?

Robert AMG

iTrader: (1)

i have also issue with idle, i got my c63 recently and the idle is always between 900 and 1100 rpm sometimes it is stable at 1000 and sometimes it plays between 900 and 1100, no fault codes in ecu/tcu, i have changed head bolts and intake gaskets, could be the pcv valve faulty but without fault code? actual values in star diagnose are below:

Cli63

900 - 1100 seems very high to me. I idle at 600 (might be cause of all the mods). What do some of you others idle at?

JordanSpaceJam

My car is doing the same thing. Its a bit rough at idle too.

65fastback

Changed the purge valve and still having idle issue, taking it to the dealer today hoping they can find the vacuum leak source within a hour....wish me luck

65fastback

Just replaced the intake manifold gaskets and still have the same idle problem..... totally bummed out. dealer said it it was a gasket leak so i assumed they were right.

so far I've changed out the purge valve and now intake gaskets. Did not see any visible cracks on the intake or throttle body.

any ideas would be welcome

ritalin

Does it seem like it's misfiring?
My car was doing that when my o2's were on there way out and fouled up the plugs causing a rought idle.

Mr. Lin

my passenger side primary did this and gave me a rough idle. but mine threw a CEL so it was easy to diagnose.

65fastback

No misfire, sometimes it will idle rough in gear. Bad or going bad 02 sensors will give a CEL if iam not mistaken?

Robert AMG

iTrader: (1)

you have internal air leak inside the intake manifold.

65fastback

Are you saying my intake has a crack or its damaged in some way? or ?

ritalin

Mine did not initially. I cant tell you how long after i experienced a rough idle the cel came on, but it was not instantaneous.

Robert AMG

iTrader: (1)

the plate that hold the throttle bodies corrode and leak air, this is what end's up with my car, the leak is inside the intake, so you will get no error codes, if the air leak is from outside let's say from the gaskets you will get lean fault code cause the volume of air leaked to the intake is not measured by the air mass flow's.

65fastback

Ok got it, sounds like you are onto something here, thanks very much for the reply.

Frankrizzo

Having the same idle issue, please keep us posted when you find the fix.

Robert AMG

iTrader: (1)

if you noticed when you look to the throttle bodies plate from the front you will notice nothing, you have to take out the plate and look behind, this is what happened in my case, first time i opened the intake and looked to the throttle bodies and everything look fine so i changed the throttle bodies without taking out the plate, then after the issue remains, i changed everything that u think about from ecu to MAF.... and lastly when i did not find the issue i decided to reopen the intake part by part then i found it.
btw car has 65k miles only.

Frankrizzo

Rob, thanks for the pics, couldn't imagine taking everything apart all over again. At least you're preventing some of us from doing the same thing . I'll be sure to check it out, hopefully it's not shot. Is it a part that can be purchased separate from the manifold assembly? If not, do you think an experienced aluminum welder could repair it?
Edit - would a catch can help prevent this issue?

Robert AMG

iTrader: (1)

Unfortunately the plate cannot be purshased alone, the entire intake has one part nb and the plate cannot also be welded, it has different type of materials (in my country I couldn't weld it).