This C320 has about 68k miles on it, with a transmission that has about 18k miles on it.

I was getting some p0170 and 171s, and experience tells me to change the MAF. So I did, and after what seemed like a life time of driving to fill the ODBII registers, life was good with no CELs. At first the ECU was confused a bit, but after a 20 or 30 miles things seems to pan out and there was no more choking or lurching.

But then the weather started to warm up a bit and the choking and lurching came back, though not quite the same. When I hit the gas hard there's a delay which wasn't happening before the MAF change. Also, another new behavior is that once the car is at operating temperature, if I shut it off for just a few minutes, especially when the weather's warm, and I restart the car it is very unhappy. Often it will stall a few times after turning over. Then once or twice it will remain OK in idle but then stall when put into gear. If tap the gas a bit as I'm putting it into gear things seem a bit better, but I feel no power from the gas tapping, just a save from the stall.

I'd start guessing a dirty fuel filter or ailing fuel pump... but all was fine, power was on tap as usual, until I changed the MAF. I'm wondering if my new MAF is bad since MAF readings are affected by temperature. Or perhaps the old MAF with its deficiencies was actually working well with the other ailing parts. I also wondered if a good ECU reset would help, but I've been driving so long on this new MAF new that I'd think the ECU has gotten used to it.

And thoughts?

 

Disconnect the MAF. If it's the MAF, the car will run fine. If you car still has problems, it wasn't the MAF.

 

Good idea. Though, I think the MAF is going to be the least likely candidate. (I got it from GermanStar and reviews of them seem to be pretty good).

 

Some aftermarket companies sometimes substitute a part the will fit but may not work correctly. For example, there's a company selling MAF's on ebay made by Bosch/Siemens but they are made for VW and while it fits and looks the same, the sensor sends our different signals and makes your car run poorly. Disconnecting your MAF will force the ECU to compensate for the missing MAF with fixed mappings and other sensors. You car will run about 90% as well as if you had a MAF but it will not exhibit the traits you are experiencing.

The second most common problem for these codes you are experiencing is a vacuum leak. I think this is the toughest to find as it can be a hairline crack on the underside of a vacuum hose. A vacuum leak will exhibit the problems you described. Just go through each vacuum hose with a fine tooth comb. Some people use a propane torch (unlit of course) and when they come near a vacuum leak, then engine revs slightly because of the additional fuel coming in.

If you are concerned about the fuel system, buy/rent/steal a fuel pressure gauge and check it at the fuel rail. Should be about 3 1/2 BAR or 50 PSI. I doubt it, you would get misfire codes if you had weak fuel pressure.

 

I've been dealing with the same issue on my 2003 C230 Sedan.

I disconnected the MAF and drove around ok... so I thought it was the MAF. But it seems now that it is a vacuum leak. I know the vicinity of the leak, because spraying carb cleaner in the area makes the engine raise its rpm.

I'm going to set several hours aside everyday and look for it.

 

Blargh, that's one thing I do not have, time. Perhaps if we put the spray nozzle straw onto the carb cleaner cap it'll be a bit more accurate. I'm too new to MB's... on my Impreza I can close my eyes and see all the vacuum lines in my mind

As for the codes, they cleared up when I replaced the MAF. The stalling problem didn't start until after I replaced the MAF, but the seemingly related symptoms of lurching and slow response to quick throttling did happen before and are now worse. _One_ time when playing around with the old MAF and clearing codes I did get a vacuum issue CEL.

You know, I just had another idea, if the vacuum hoses can suck in propane and carb cleaner, why not just list some incense and follow the smoke? I'd test first with the carb cleaner to hear the engine rev up to at least confirm some leak somewhere and then try to pin point it with the smoke.

 

Interesting thread.
But yeh, there's an old saying when working on cars.
If you change a part and new symptoms appear,
Always go back to the last thing you did.

 

try spraying the EGR valve on the back of the right head, spray the shaft of it... and watch is boggg

 

If this was a vacuum leak issue, wouldn't the bogging problem show with both MAFs?