c240 revs to 4.5k then starts to miss/rough idle

[rotaxman]

Hi All,1st merc and first post,,after starting searching here today,i fixed the heater intermittant issue,,£134.00 from dealer for fan regulater.ouch should have searched better on the web for parts.
my c240 v6 starts fine when cold but if i let it rev above 4.5k it will start to miss then will rough idle and be even more gutless than it already is,sometimes just gets me home,although if i keep the revs below 4.5,,all is well..the car is also a pain to start when warm,,i have to keep taking key out and trying again.then it will start and all will be fine ,as long as i dont rev over 4.5k..could this be the mas,,or maybe plugs,,,105k miles on her and there was no air filter in the box (rectified this immeadiatly),doing oil and filters a weekend,also tranny fluid too
this merc c240 sport is SO much slower than my wifes mondy v6,should it be ??
suggestions please..
cheers
Shaun

 

[jberks]

Hi,
Firstly, I couldn't find a new regulator outside the dealership network so I wouldn't beat yourself up too much on that one.

Secondly, if it starts to run badly once you've revved over 4.5k it sounds like it's going into emergency mode which simply means it's detected a fault. You could muck about changing stuff and it probably is the MAS, especially if she's been running without an air filter (and almost certainly not the plugs) but for the cost of getting the ECU interrogated to pick out the fault code, I'd do that first. It does sound like she's been a little neglected and if someone has been running her without a filter I'd be suspicious as to why, so personally I'd have a reputable specialist giver her the once over. It may cost £50-100 but she's a complex motor and an experienced eye, equipped with a startac machine could save you a great deal of hassle later.

She's probably a bit slower than a mondy but then she's built for long distance cruising rather than the drag off the line. I find the 240 v6 a bit 'average' below 3.5k but quite lively above, but as your's runs out of steam at 4.5k you won't have found this out yet! Suffice to say that mine (heavier) will happily sit up hill and down dale at well over 100 if I let her, and infact she's livelier above 80 than below. Booted she'll keep up with most opponents, but they don't have the ride, silence and build quality we do!.

 

[rotaxman]

sorted it cheers fellow postees

today I have changed the oil filter and the oil,(ouch that was dear,mobil 1. 8 litres),also removed the maf,cleaned it good with carb cleaner spray,added injector treatment to petrol,,italian thrash down motorway,runs very nice now,revs past 4.5k and no rough idle,,,just need to change the atf fluid now and the plugs (hmm not looking forward to doing this,but I hate paying for something I can do).
thanks to all the posts I have read they helped a lot,
cheers
:lol: