220TE rough running, sometimes

[DenisM]

Hi

I have a L reg 220 Te which for the most part, runs well ans is very comfortable.

From time to time, generally after I have slowed down, the engine spped goes up and down. If I am stopped you can see the revs going up and down, or hunting ? The difference is not vast, say max 500 rpm, but enough to notice.

If I am driving, then the speed goes up and down even with constant pressure on accelerator pedal.

If I switch off engine, and restart it appears to clear problem, or if I start driving at speed then problem goes away.


Any one please suggest my best course of action to find the fault.

Thanks

Denis

 

[roofless]

if it's only when warm at idle it will prob be the regeneration valve sticking open to test just blank off the vac pipe at the engine side

 

[jibcl500]

Check the condition of you engine loom, next to the battery on the left side there is a 2 pin plug, one wire is green the other cant remember but that plug lies in any water that sits there and causes a short, if the plug is green with copper rot then thats the start of all your worries, the loom that runs to the MAF, handle that loom with the engine running and if the engine stalls or ticks over rough then the loom is had it.
Change the loom before it shorts out the OVP destroys the MAF, I have a loom if required.

jib

 

[television]

I feel it is a vacuum leak, that the most common fault, the pipes must be tight and no splits. also as roofless posted that valve can do it

 

[DenisM]

if it's only when warm at idle it will prob be the regeneration valve sticking open to test just blank off the vac pipe at the engine side View attachment 7171

Thanks for your suggestion, but what will be the result of blanking off the pipe ? Will it run perfectly or will it be rough ?

 

[television]

Just blank it off and see what happens, you cannot do any harm

 

[DenisM]

Thanks for your suggestions. I have just got back from trip to Scotland (800 miles) and it cruises fine on motorway, I just have problems at slower speeds. Fuel consumption is fine, over 30mpg cruising at 72 mph for most of time.

I have now checked out your suggestions and have found following

1) everything round battery is clean and tidy and is tied nicely down. I have tried moving anything that moves and it makes no difference.

2) with engine revs going up and down I removed pipes from valve one by one and put thumb over end of pipe and does not make any difference. Valve appears to be working because I can hear it and feel it opening and closing.

I also removed plug off top and engine continues to go up and down.

3) If I start engine it idles fine at about 900 rpm. If i then depress accelerator so it revs at about 3000, then release it engine speed dies back (as you would expect) to around 1000 rpm, but it then goes up and down between about 800 and 1100 rpm.

If I switch engine off and restart it idle is fine....

4) A related observation/question - I recently almost ran out of fuel, could I have picked up some water/dirt which is now causing problem ?

I have had bikes/cars when dirt has got into filter/carb and at higher revs there is enough pressure to pull fuel through but not at lowers revs. Could this be problem ?

Thanks for your help

Denis

 

[teddycatkin]

Could be the OVP breaking down ? (capacitors)

 

[roofless]

the only thing other than as jib said w-loom would be the micro switch at the throttle stop just check the throttle returns & makes contact with the switch with the engine off you can hear it click when you move the throttle slightly by hand open & shut

 

[DenisM]

Could be the OVP breaking down ? (capacitors)

Sorry to show my ignorance, what is OVP, where do I find them, and can I test them or do I just replace ?

 

[DenisM]

the only thing other than as jib said w-loom would be the micro switch at the throttle stop just check the throttle returns & makes contact with the switch with the engine off you can hear it click when you move the throttle slightly by hand open & shut View attachment 7215

Thanks for suggestion - i'll try tomorrow in daylight.

 

[Bolide]

I'd say dirty throttle body. Get the carb cleaner on that butterfly!

Nick Froome
www.w124.co.uk

 

[DenisM]

Thanks to everyone

Well thanks to everyone - I checked the micro switch and it was not switching at all. So I adjusted the rod linking it to accerator cable and it now works.

Engine now nice and smooth.

I also cleaned butterfly valve but it appeared clean.

So thanks again to everyone - I'll try and help answer some questions, but I need to learn lots about the merc.

Denis

 

[DenisM]

Running rough again

Hi Everyone

Since last posting about my rough running, I have made some progress, but now it is running rough again at speeds below 30mph.

I've done the following in addition to bits posted before

1) changed plugs and leads (a couple were looking corroded)

I left plug gap at .8 as delivered. Is this correct gap ?

2) I changed fuel filter

3) I cleaned butterfly valve with carb cleaner. Everything then appeared to be fine after.

Having gone out with my wife it started running rough after about 30 miles. On reaching our destination I checked under bonnet and air intake pipe to butterfly valve had become detached, I reattached and it coughed and spluutered a bit on way home.

4) I recleaned butterfly valve as I thought pipe coming off would have made it dirty again.

If anything it is now worse, it coughs and splutters below about 30 mph and appears ok after.


Near the front left headlight there is some sort of electric valve in a vacuum line. It was working before because I could hear it clicking on and off. I can't now hear it. Could this be the problem ? Is there any way of testing it ?

I have tried removing vacuum pipes, one at a time. If I remove one on vacuum side then engine almosts cuts out. If I remove other it appears to make no dfifference. If I put volt meter across incoming leads I don't appear to get a change in voltage when I rev engine, what reading should I get ?

Any suggestions please ?

If all else fails can anyone recommend a Mercedes engineer near Oxford to look at it ?

Ta for your help

Denis

 

[Number_Cruncher]

>>Mercedes engineer near Oxford

I don't think you mean engineer. Mechanic, yes; technician, possibly; but, engineer, I doubt it.

 

[DenisM]

>>Mercedes engineer near Oxford

I don't think you mean engineer. Mechanic, yes; technician, possibly; but, engineer, I doubt it.

Agreed, thanks Number_Cruncher

 

[kth286]

Denis

when you say the intake pipe to the butterfly valve I take it you are talking about the large pipe over the top of the engine ?

If so how did you re-attach it ?

 

[Alex Crow]

oh dear, and it was all going so well! can we confirm this is a hfm model and not the pms (i think it must be).

denis, have you got a plastic device with circular electrical connector which is mounted between the air filter and this intake pipe, with the intake air passing through it? if so it is vital that there are no leaks between this sensor and the throttle body, if you have air getting in here then that will likely give the new symptoms you describe.

 

[DenisM]

Thanks for reply

Denis

when you say the intake pipe to the butterfly valve I take it you are talking about the large pipe over the top of the engine ?

If so how did you re-attach it ?

Yes I mean the large pipe. I reattached it with jubilee clips.

I have attached picture, which I hope is clear enough

Denis

 

[DenisM]

Air intake

Thanks for reply. Picture with my last post.

oh dear, and it was all going so well! can we confirm this is a hfm model and not the pms (i think it must be).

Sorry, but what is hfm and pms ?

denis, have you got a plastic device with circular electrical connector which is mounted between the air filter and this intake pipe, with the intake air passing through it? if so it is vital that there are no leaks between this sensor and the throttle body, if you have air getting in here then that will likely give the new symptoms you describe.

Yes I have - I have taken electrical connection off, but not taken sensor out. I realise this does not mean it is not leaking.

Is there any way of testing sensor ? If I remove ecectrical connector will it do any harm ? I can then see if anything alters.

I have also got hold of drawings on MB website and worked out that valve I refered to in my long post is a 'Regeneration Valve' but I can't work out what its purpose is, any ideas please ?

Mean while I'll try and see if there are any air leaks.

Denis