C320 Issue (maybe plugs, maybe something else)

[sac122]

Hi guys, I need some help and I was wondering if you can assist?

I recently, approx 3 months ago, bought my first Mercedes, a 2002 C320 Avantgarde (lovely btw) and I have enjoyed it immensely but in the last week I've had some problems.

First I noticed that the climate control wasn't cooling down and only blowing hot air (I thought it might just need recharging), fuel economy seemed to be dropping slightly. One morning however I went to pull away from a junction and I had a loss of power (misfire) which then steadily came back as I drove down the road. At this point the engine management light came on and stayed on. The rest of the journey, 10 miles, was uneventful although the engine was running rough while idling.

By the time I got the car to a garage and onto a diagnostic machine, 48 hours later, the light had cancelled. Diagnostics showed a misfire across the cylinders with number 2 most common and a fault on the MAF sensor.

As the fault wasn't current or "reproducible" whilst in their possession the garage was reluctant to offer a solution. Frustrating though understandable.

They did mention some possible faults including spark plugs, coils (these can be damaged quite easily) or MAF sensor. Total cost of which was sizeable with no guarantee of a solution.

Since being on the machine the car has run smoothly until this morning when it has misfired all the way to work and the engine management light has come on again.

Anybody got any thoughts on what might be the cause?

Cheers

 

[BlackC55]

The air mass sensor is the most likely cause.

 

[jberks]

Change the MAS - misfire and poor idle are symptoms of safe mode caused by a MAS misread. Price one up from your dealer and also check if you can get the insert from a Bosch dealer (often substantially cheaper). I doubt its a coil as it's intermittent and almost certainly not plugs as its a twin spark and you have to lose both to get a bad misfile (one just makes the idle a bit lumpy).

 

[BlackC55]

Change the MAS - misfire and poor idle are symptoms of safe mode caused by a MAS misread. Price one up from your dealer and also check if you can get the insert from a Bosch dealer (often substantially cheaper). I doubt its a coil as it's intermittent and almost certainly not plugs as its a twin spark and you have to lose both to get a bad misfile (one just makes the idle a bit lumpy).

A lumpy idle on a V6 112 engine is a missfire.

Plugs can cause missfire's on these. Very common as people do not want to fork out for plugs when they are due as it is quite expensive. So they get left till it missfires.

 

[sac122]

Update and thanks

Thanks for your advice so far guys.

Yesterday I opted to change the plugs (mainly because it was much cheaper than changing the MAS) and everything was fine on the way home.

Unfortunately the problem recreated itself this morning, loss of power, very lumpy idle and the return of dreaded engine management light, which I expect to self cancel at some point in the next 24 hours. I switched off the ignition at the next junction and restarted which removed some of the lumpiness but power still seems restricted.

So I'm going to change the MAS sensor latter this week which I hope will finally sort all of this out!

Once again, thanks for all your advice, without it I wouldn't have a clue what was wrong or how to move forward.

Cheers guys, I really appreciate it.

 

[television]

Buy your MAF from Bosch,more than ½ the price of MB, any Bosch services center has them