Hey all,

Did some work yesterday to fit the C320 engine cover with fiters, 3'' MAF and 74MM TB.

Connected all up and went for a drive. Noticed the revs started to rise to 2K when in neutral (manual trans) but moving. As soon as the car is not moving the revs drop to idle.

Plugged in the ECU reader and it shows the throttle position is rising from .8 to 3 then back down to .8, causing the revs to go up and down.

A quick question - the double pipe connector at the end of the throttle body, should they both be plugged in for an NA? One of mine looks rusty to the point where it looks like no tube has ever gone on it. I'm wondering if thats somehow causing the problem.

I dont think its a vacuum leak, certainly couldnt see anything - but if that pipe isnt the problem then I'm not sure...

 

Yes, one is for the evap solenoid tube, the other for the joined valve cover breather tubes.

 

Not to ask the obvious but how many hoses were on the old TB?
If you say two then you have your answer.
If you only have one on the TB that is a vacuum leak of the highest magnitude.

 

If I knew the answer to that question I wouldnt be asking how many should be attached

When removing I didnt see the hose connection closest to the engine block. I did connect it however as it would be mighty strange to have 2 pipes and 2 connectors with only one plugged in.

I'm wondering if the MAF sensor is faulty.

 

I hope that you swapped in the OEM maf sensor with the maf housing upgrade..

 

Ah I uh, forgot! Swapped over tonight but I haven't started the car yet.

Although I am a bit surprised as it seems that both the 3' and 2.5' maf sensors have the same part numbers?

Defo got the right maf, correct part number and bigger diameter.

 

Not sure what or where you bought.. but most of us buy the 30 dollar or so housing that typically has some china knock off in it.. or sub par sensor.

 

Are you sure they are the same? I suspect the original number is A 112 094 00 04, and the new one is A 113 094 00 04.
Just a guess though.

 

Definitely the right maf. I bought it from an eBay seller from Germany. Brand new bosh unit with bosh sensor.

The housing has a different diameter, I.e no additional restrictive housing, and it also doesn't have those ridges the 2.5 maf housing has. It's just the sensor looks the same, both visually and part number wise!

 

I bought this one:

Mercedes-Benz Air Mass Sensor - BOSCH - 0280217810 / 1130940048 - NEW MB MAF | eBay

Defo the E55 AMG V8 variant! I can't seem to find the part number for the actual sensor anyway, so maybe the part number is linked to the housing part number?

 

So I replaced the sensor with the one from the original MAF and it seemed better for almost 2 hours before starting to hunt again! It did it properly twice, then for the rest of driving nudged up a tiny amount when letting off the revs.

How annoying!

The fact it got a tad better might be due to either the sensor being naff or because I removed the engine cover and reseated it, perhaps its not on properly. I'm going to investigate more over the weekend and see what I can do.

 

Same thing happened to me I don't know what to do.

 

What checks have you done?

I've now checked all the pipes and reseated everything. Replaced the sensor as well.

The hunting still occurs and now I think I'm getting over-fueling (or a blown CHG).

I think I'm going to swap out my throttle body for the original and see if that helps.

 

Replaced the sensor? It is not clear what sensor you are using now, old one or the new one.
The MAF housings have different part numbers, one starts with 112 and the other 113. Mercedes does not have different parts with the same number.
Here is a post that shows the different MAF housings and sensors.
As far as I recall when I switched the sensors they were different. The sensor from the larger MAF does not have a Mercedes number on it, just BOSCH numbers.

 

I used the same sensor with same housing I checked the hoses the only thing I'm mind is that probably my o ring slipped or I messed up the maf sensor when I cleaned it with the crc cleaner. I will try to take it apart again and see if the o ring its ok

 

Sorry, I wasn't very clear.

Using the guide you linked I swapped over the throttle body, MAF and used a C320 airbox to upgrade to the 74mm TB and 3'' MAF.

Initially I didnt swap the MAF sensor as they have the same part number on them. The MAF is 100% the 3'' version as that additional second layering it doesnt have.

I then swapped the MAF sensor for the original one that was in the 2.5'' MAF.

It didnt make any difference unfortunately.

Yesterday I took a very long look at the system to see what could be wrong. Everything is connected and there are no breaks/rips in any lines. All conectors look sound and nothing is damaged from what I can see.

However I did notice that when the engine cover is pressed onto the 4 catches, the MAF does not sit snuggly inside the engine cover like it should do. It seems to sit with a 2-3cm gap towards the cabin.

I tried and tried to make it line up but was not able too. I got as close as I could get and took it for a drive, found that the car has a flat spot at around 3.5K RPM and when checking after, the gap had increased.

HOWEVER

Today I reversed the process of fitting, instead of attaching the MAF then the engine cover, instead the engine cover to the MAF and then to the throttle body. The cover is sitting tightly on the MAF and on the engine.

Took it for a short drive, got her nice and warmed up, it hunted once slightly.

I'll take it for a proper drive tomorrow if I can find time and report on how it goes. What confuses me is that the throttle position rises, as if its ECU controlled increase, faulty signel from the pedal or a faulty sensor.

 

Just to follow up a few months later, issue gone and car running perfectly - guess it was just equalizing to mods.

 

This has been an issue with several upgrades. Our computer is very sophisticated and can learn, though it takes a little time. I had that issue when I modified my exhaust, it would send a lean condition CEL until it learned and adjusted.