Surging and miss firing after MOT.

[jfhuk]

My E350 was in for its MOT on Tuesday, which it passed. Since then though it's been surging and miss firing particularly when the engine is cold. I realise it could be a coincidence, but is there anything that the MOT could have done to cause this sort of issue? As prior to the test it was fine.

 

[brucemillar]

They "may" have disturbed a vac hose or plug lead. The engine bay is usually a visual check with some light pulling to make sure nothing is falling off. They "may" have accidentally pulled something off.

I would give it a good look over and tug on any hoses, plug leads etc that you can see. That is what they should have done as they do not remove covers etc.

 

[jfhuk]

Thanks the MAF sensor cable on drivers side was not fully connected. Reseating it seems to have cured it.

 

[camerafodder]

...and that's what you call a Brucey Bonus!

 

[brucemillar]

...and that's what you call a Brucey Bonus!

Cuddly Toy, Cuddly Toy? :^)

 

[jfhuk]

Look at the old score board... Didn't he do well!

 

[optimusprime]

You should have a first prize for that.

 

[jfhuk]

May of spoke too soon the miss firing is back unfortunately. Mercedes Roadside assistance found a MAF hot film mass flow sensor has a plausibility error on his xentry unit. He tested both MAF sensors using the xentry and both passed. Fault frequency only showed one error. Guess it will require trip to stealer 8-(

 

[def90cars]

They "may" have disturbed a vac hose or plug lead. The engine bay is usually a visual check with some light pulling to make sure nothing is falling off. They "may" have accidentally pulled something off.

I would give it a good look over and tug on any hoses, plug leads etc that you can see. That is what they should have done as they do not remove covers etc.

Not allowed to do that..... fuel leaks only really.

 

[jfhuk]

Car is off to dealers, as the yellow engine warning light came on today and it's still miss firing 8-( Mercedes are arranging loan car.

 

[brucemillar]

Be interested to hear what the dealer finds? Good luck.

Tony is correct. MOT testers are not allowed to randomly pull things about. But they often do. Not to be malicious. But, as with any engine bay, when looking for fuel leaks, loose battery etc it can happen that something else gets disturbed.

In your case, given the problem started at MOT time, it would be a reasonable conclusion that this may have been the case.

 

[Rory]

Hate taking my car to the garage - mine came back from its recent trip to the dealer with a very subtle vibration through the car which I first thought might be because they'd dropped the tyre pressures on the All Season tyres. Then I realised it was doing it at idle too.

 

[jfhuk]

The latest is that the car is supposed to be on diagnosis, I've heard nothing back so far, which sounds a little worrying.

 

[jfhuk]

After diagnosis it appears it's a MAF airflow sensor issue. Being Mercedes they want to replace the whole MAF unit including both sensors and the trunking! Dealer is asking Mercedes for a contribution as its just coming up to being four years old.

Seems crazy that you can't just replace the duff sensor..

 

[jfhuk]

After a fair few calls by me and a lot of emails from the dealer, we managed to get Mercedes UK to pay 60% of the fix costs as a 'good will gesture'.

An email to the factory support just got a one word reply of no.