Uneven Idle

[Larry]

I own a 98 E240, V6, with 70K miles on the clock. I know the complete history of this car, as it was previously owned by a family member from new. I have lately experienced an intermittent uneven idle. This has happened between services. Revs haven't dropped, nobody has tampered with the engine. I decided to try to eliminate possible causes. Firstly I changed all 12 spark plugs. All old plugs were same colour, no unnatural deposits. New platinum tipped plugs fitted, pre-gapped, but meticulously checked. Result : No difference to idle, but generally more responsive driving. I then changed the fuel filter, draining residual fuel onto white paper, result, no sediment, idle still the same, uneven ? Air filter is recent, oil changed every 8K,[ I don't believe in long oil change intervals] running on full synthetic, doesn't use any between changes, so I doubt sticky valves. Local MOT garage checked emissions and vac system to eliminate Cat or Lambda probe problems, very low emissions, not changed ,comparing last four MOT figures. Coolant level never alters, engine oil clean, golden, so I doubt blown head gasket. I have come to the conclusion that I may have a problem, either with a coil pack, or maybe the air control unit, however when running, car performs normal, no misfires, even under extreme load. How can these be eliminated? The only other piece of info I can give, is that the fuel pump relay [red one, under rear seat] seems to run quite hot, is this normal ? How can I eliminate these items, i.e: what symptoms could these three items give, if faulty ?

I have spoken to various local specialists, some of whom tell me that even though they have diagnosis equipment, it may not pinpoint the fault, i.e: it may say there is a misfire, but not where ? This would then put us back to the process of elimination ! Can anyone give me any advice other than: go to a Mercedes dealer ? The only one I have found helpful in the past, in my area, has been the former Drake and Fletcher, Maidstone.

I have one other problem. The w/s switch on the gearbox no longer switches into "S" mode. Is there a relay for this operation, as I could find no relevant fuse in any of the three fuse compartments ?

 

[jberks]

Hi Larry,
Welcome to my world!
I've had one success about three years ago with this. It turned out to be the plug leads that had corroded on the inside. New set and sweet as a nut. Its been fine since until about 6 weeks ago when it started again. I too put new plugs in which eased it a little but not enough. It was pretty awful until I realised that the plug leads click on. Its a b'stard to do as they are very, very tight but if they don't click, you will get an occasional miss.
Now I find that 25% of the time, she's absolutely perfect, 50% slightly lumpy but probably acceptable and the rest, a bag of spanners.

A couple of points.
1) Forget the dealer. It will cost you a fortune and very doubtful you will get a solution.
2) Most garages rely on the computer - as you say, this will not show up on the diagnostic. I went through this loop a few times. I even had a couple of 'They all do that' comments. (that was at 25k and 3 years so I refused to accept it) They dont - or at least the non faulty or worn ones don't !.

What I did in the end, was get my local specialist to agree something wasn't right, then book it in with a loan car. I told them to keep it as long as they wanted but I didn't want it back until it was perfect - pretty much a blank cheque job, but they are honest so I knew I wouldn't get ripped off. The beauty of the specialist is that they can try bits without charging you for the parts - so £45 for an hour's mucking about, rather than £90 labout plus a £250 part that you didn't need.

Plus at half the cost for labour, on an unknown issue you could be saving a fortune. Also, specialists are more likely to charge you a fair price, rather than for every second, so if its something daft you aren't going to pay full whack whilst they muck around with all the complex stuff. They are also more familiar with a car the age and mileage of yours, the dealer's mechanics rarely see anything older that 3-4 years. They tried a new throttle body and a couple of other things before they found the culprit. It took 4 days too. Total bill was around £400, but that included over £200!! for the leads. But then that would only cover 4 hours at the dealer, not 4 days diagnostic plus parts, so still a fair price.

I intend to do something similar again, but this week she's been sweet as a nut, so I may have to wait until the winter. She seems happier when the air is warm for some reason. The fault is more consistent when cold in cold air.

 

[jerry1]

Larry this is exactly my experience and I still have an uneven idle after 12 new plugs via my local dealer, who eventually wanted to try an engine management unit £870 before fit. I declined. I am now coming up to a service my C240 is nearly 5 years old and I came on to the site to ask if anyone had serviced their car at a French dealer, what was their experience and to also see if they could resolve my idle problem.

 

[jberks]

Jerry,
Do yourself a favour. I understand that there are a lot of excellent MB specialists in London. Most will be able to sort your problem, without the hassle of trecking across to france and for a similar cost. -

I have heard about the france service idea - great in principle, but how many times have you had to go back a few days later, either for something that isn't right, or for a part they didn't have in stock. Often a service isn't a 1 day trip and you quickly burn up the saving in petrol and ferry/chunnel fares.

In any case, out of the question though for us northerners!- we are too backward for a decent rail link to the chunnel - Then again, I guess we need electricity and inside toilets first ! - Must go - the wippets run off with me flat cap...

 

[jerry1]

I was hoping to kill 2 birds as the saying goes by getting a service and a new set of eyes on my dodgy tick-over. I keep thinking that how complicated can it be when everything works fine, even with a cold start for a small distance the tick-over is fine but after that it is unpredictable as to how bad the idle will be. So I need to take it to a MB specialist near me (I live in Enfield ) who I can trust will treat me fairly and service my car what about the stamp?

 

[Larry]

Thanks for advice.Have since found out that new set of plug leads[ x12] are £90. Coil packs are £105 each [ x6]. Car running smooth at moment, must be the weather.Driving to Spain soon, so will gather info from a dealer I know there.

 

[Last Lightning]

Just cured a similar problem with mine (280e) started ok in the mornings for about 10 minutes then ran like a bag of spanners then eventualy quits altogether. I took the airfilter box off and cleaned out all the breather pipes it now runs and sounds absolutely spot on :smile:

 

[jerry1]

Thanks L.L. mine runs like a dream it just will not tick over evenly. I can however understand your elation at having solved your problem all suggestions welcomed.

 

[jberks]

Thanks for advice.Have since found out that new set of plug leads[ x12] are £90. Coil packs are £105 each [ x6]. Car running smooth at moment, must be the weather.Driving to Spain soon, so will gather info from a dealer I know there.

Larry,
Hate to disappoint you but plug leads, or at least official ones, are over £200 for a set! I'm not sure I would use non MB ones as they seem very sensitive about these things - not that I have come across any. Yes plugs are £90. I put in NGK irridium ones at about £110, though not sure if there is any benefit. By the way, installing the plugs is a bugger. Took me 2 1/2 hours and a lot of unpleasant language and the scars on my arm are still healing. Most plugs are very difficult to get a socket to, let alone turn it when you get there. It made the £250 quote from the garage seem very reasonable.
And the poor idle is still with me.
I am about to go on holiday so I think my local indie is going to get an E class to play with for a couple of weeks!
JB

 

[jberks]

I was hoping to kill 2 birds as the saying goes by getting a service and a new set of eyes on my dodgy tick-over. I keep thinking that how complicated can it be when everything works fine, even with a cold start for a small distance the tick-over is fine but after that it is unpredictable as to how bad the idle will be. So I need to take it to a MB specialist near me (I live in Enfield ) who I can trust will treat me fairly and service my car what about the stamp?

Jerry,
My views on this are well known on this forum - having just collected my W210 from the dealer, after having what must have been £1500+ of bodywork done (and a beautiful job they did too), FOC courtesy of MB, I am a firm believer in keeping your dealer sweet and an FMBSH running.
At the same time, my idle issue is going back to the specialist that cured it 3 years ago - cheaper and probably better skilled. Its a bit of a pain using 2 garages but aside from the service every 16,000 miles or so, all other issues go to the indie as its a hell of a lot cheaper. Especially with issues that can't easily be identified as they may take a lot of time and trial and error before they find it. Specialists tend to charge similar prices for parts to the dealer, but being a time issue, a £45 per hour saving isn't to be sniffed at.
As far as trust goes, indies live or die on reputation and people on here will be happy to recommend experts in your area. Do use an MB specialist though as the kit and knowledge required can't normally be found at a 'normal' garage. good luck
JB

 

[jberks]

Update

Hi all,
Just back from Hols and E240 back from MercCare. Handed it in when I went away and asked them to run it themselves for a week or so to find the problem. It took a couple of days before she misbehaved enough to diagnose apparently.
New HT leads fitted (again) and she's back to sweet. No juddering when creeping and no intermittent lumpy idle. 3 years and 30k ago I put the first set in so that seems to be the lifespan - at least for me. The firt set set were visibly corroded, the 2nd looked fine but clearly weren't. £250 a shot is damned expensive for parts that only perform properly for 3 years at a time, but I have my old car back again - at least for another 3 years!