Likely MAS/ECU issue?

[Steve_Perry]

Shude,

I am intrigued by your attached diagram, I can see that the part you have highlighted is the MAS sensor but what is part No. 5 in the schematic?? It looks suspiciously like a 2nd MAS unit.

S.

 

[Shude]

I am intrigued by your attached diagram, I can see that the part you have highlighted is the MAS sensor but what is part No. 5 in the schematic?? It looks suspiciously like a 2nd MAS unit.

It is another MAS sensor with an almost identical part number. The scary thing is that the EPC would let me order either of them for my car without problem, both numbers seem legit.

I don't think there are two on my car so what's the story?

 

[GregE240]

Nick, different engine but EXACTLY the same symptoms I had on my 210 when the MAS went south.

Similar to Steves PVS problem, my MAS wasn't showing up any errors, but swapping out with a known good one transformed the car. It had a new MAS at 98K (now on 129) and has been good as gold ever since.

Have you had your gearbox oil replaced at any time? With that sort of mileage, you should be thinking about it.....

Greg

 

[Steve_Perry]

It is another MAS sensor with an almost identical part number. The scary thing is that the EPC would let me order either of them for my car without problem, both numbers seem legit.

I don't think there are two on my car so what's the story?

Could it be to do with relocating the MAS sensor on the 230K engine after '99? Didn't you post something about the old position is close to the air filter box but the new position is elsewhere, giving a 4BHP increase?

S.

 

[RAV]

I had similar problems but without the gear issues on my father's C220 (1995). The symptoms were intermittant (and very frustrating which is why I started to search for this kind of website):

a) It would run on two cylinders
b) Initially turning the engine off and re-starting again it was fine. but this got gradually worse and did not resolve the problem after a while (couple of weeks)
c) I think the fault codes pointed to the igition coil but this was replaced to no avail. (it worked from the garage to near the house!)
d) It would shake and initially you could move it (on low power) whilst on two cyclinders but later it just cut out.

The problem was fixed by repairing the ECU rather than replacing it. This cost about a quarter of the £1000 MB part. Further info can provided if requested.

 

[Shude]

Have you had your gearbox oil replaced at any time? With that sort of mileage, you should be thinking about it...

I'm not going to do anything with the gearbox, even the local bosch-service independent garage said they won't touch them!

The gearshift problem is related to the fact that in order to make any progress with the half the engine not working the gas pedal has to be about 2/3 down. The gearbox computer thinks I'm trying to get it to shift down so it basically holds it in gear or shifts down at the wrong time. I'm not going to worry about the gearbox for the time being, it's basically trying to do it's job.

 

[GregE240]

So you don't plan to change the ATF any time soon?

Blimey...hope you've got 2 grand kicking around. I'm not suggesting this is any way MAS related, but once the fluids changed the gear changes are so much smoother. And when you see the state of the fluid that comes out of the box, well.....

 

[Shude]

So you don't plan to change the ATF any time soon?

Not currently planned.

Blimey...hope you've got 2 grand kicking around. I'm not suggesting this is any way MAS related, but once the fluids changed the gear changes are so much smoother. And when you see the state of the fluid that comes out of the box, well.....

The gearbox has never shown any issues and my previous car's gearbox was fine at 150k.

AFAIK the ones to watch are the very early gearboxes from 1997, by 1999 they were making the good ones

 

[GregE240]

Fair enough, Nick. Noticed on another thread on here someone was looking at having theirs changed for the first time at 197K.

 

[Shude]

ok, the stealership say:

231.98 +VAT = 272.58

for just the MAS, no fitting or anything.

 

[rizal2510]

My w202 MAS also went this week, symptoms are lack of power and stalling when braking to a stop hence dreading a stop and go traffic situation. Went to a mate's with star-diagnose and came out with MAS failure..luckily he had one lying around from another car so I put it in my car first until I could find a cheaper source of MAS...

 

[Shude]

My w202 MAS also went this week, symptoms are lack of power and stalling when braking to a stop hence dreading a stop and go traffic situation.

In stop-and-go traffic I've got really fast at stopping/starting the engine! Works fine at low RPM/low speed. I can rev it while stationary and it's no problem. Try to get it to do anything at about 30mph+ and I assume the amount of air going past the MAS causes it to panic the ECU or something and it goes crazy again.

 

[nickmann]

Because of the gearchange issues I'm having and the suggestion that it may be the MAS, I just tried an experiment. I disconnected the MAS and went for a drive. Here's what I noted when itwas DISconnected-

There is a slight hesitation at about 1100rpm on blipping the throttle
Engine revs rise and fall faster, as if running a touch rich
Threre is a slight hesitation at about 1100rpm on setting off
No engine warning lights
Slight (20hp?) loss of power
revs well to 5000rpm
No loss of kickdown
After a couple of miles I stopped, reconnected the MAS and all is back to normal.

I therefore think that a failING MAS sends erroneous signals to the ECU, but a failED MAS sends nothing, so the ECU ignores it. Perhaps the final test would be to physically disconnect the MAS on a car that is "playing up"?

 

[Shude]

I therefore think that a failING MAS sends erroneous signals to the ECU, but a failED MAS sends nothing, so the ECU ignores it. Perhaps the final test would be to physically disconnect the MAS on a car that is "playing up"?

I will try that! If it behaves as you say then I will take out the existing one, see if it looks damaged or dirty in any way (like a leaf wrapped around it or something!) and possibly replace it with the one I know they have in stock at Whitefield.

Thanks for the info!

Someone needs to either come up with an aftermarket solution or perhaps just a box which emulates the normal MAS data in the event of it failing!

 

[R2D2]

Leaves, remember a couple of weeks ago my wife's car was playing up and that turned out to be a leave in the airfilter. Blooming leaves!

 

[Shude]

Leaves, remember a couple of weeks ago my wife's car was playing up and that turned out to be a leave in the airfilter. Blooming leaves!

I found a leaf inside my interior ventilation fan a while ago. HOW did it get past all the various filters etc?

Leaves are evil.

 

[R2D2]

It does defy logic that a whole leaf can go through vents, grills, tubes, filters and end up in the gubbins!


EDIT. I bet main dealers plant them there!

 

[Shude]

EDIT. I bet main dealers plant them there!

no puns intended?

check the leaves for part numbers!

 

[Shude]

Car is at the stealership for a B-service, and diagnostic of the MAS or whatever fault.

The geniuses in the workshop have diagnosed it as spark plugs.

Sure! What are the chances that they change them and it makes no difference? I said they can change them anyway (not too expensive) but I can pretty much guarantee it won't fix the problem!

We shall see...

 

[Shude]

How wrong was I?

It was the sparks!

Full marks to whitefield for working it out.