W124 E200 unstable idling

[guzzler]

Hi,

New member and am looking for help. My 1994 E200 has 95000 miles on the clock and runs very well and has never given trouble. This weekend though when in neutral the idling has become erratic and if I rev to 2000rpm there is a fair amount of vibration and possibly misfiring. I couldn't get my mechanic out to look at it but he said to change the spark plugs to see if that made any difference. Job done and the car ran fine for a while but now the problem has returned. The car will drive but is sluggish and will stall easily. The only thing I can think of is I may have run the car longer than I should have with the petrol tank reserve light on and maybe doing that has caused some sort ot blockage somewhere in the fuel system.

If anyone has any thoughts I would appreciate it. Thanks.

Guzzler, Dublin.

 

[JamieD]

does the engine sound 'normal' but lacking performance or is it misfiring?

 

[guzzler]

hi jamieD, thanks for your reply. Yes the engine does sound normal and performance has detoriated. I am pretty sure its not misfiring. I am in work and just went out to start it. It's been parked since 3pm now 6hrs. Initially it's fine idling steady at about 950rpm. Drove it around for a few minutes same problem returns. The tachometer oscillates between 700 and 800rpm by itself when in neutral. And it doesn't like being revved. Again at 2000 or 2500 lot of vibration. Also the exhaust while not being smoky it is a bit sooty but that may not mean anything. Maybe a full tank of fuel with some engine cleaner type additive might help.

Thing is I'm working in a pub finishing late and wondering am I taking a chance trying to get it home or will it let me down or could I be doing further damage by driving it at all.

Cheers, guzzler

 

[television]

It sounds like the infamous ECU is going down when warm causing a missfire on one or two cylinders, it will get you home with no more damage. there is another thread running on the same issue, will try and answer more later

malcolm

 

[guzzler]

Hi malcolm, my mechanic has looked at the car this morning and is in agreement. Problem is he can't get a loan of an ECU to be 100% sure. If I commit to buying the ECU, the price quoted is €1700 incl vat about £1160. Suppose I will have to take the leap of faith.
Thanks. Dave

 

[jberks]

Dave, Your existing ECU can be removed, tested and if necessary, repaired. There are lots of firms that do this now, just google ECU repair. There is no need to buy a replacement.

 

[television]

I have not seen one of these, but have read about the problems, I did explain in the other thread what happens.
the units contain output transistors that drive the coil packs, all output transistors that supply large currents get hot, and the heat is dissapated through a heat sink. (on a heat sink, the heat disspurses to the outer edges, maybe you have seen the fins that increase the cooling area)
When the transistor has lost contact with the heat sink (heat sink compound is used) thermal runaway takes place to the point where the output of the transistor drops to zero. the output term is HFE. when allowed to cool down the cycle repeats itself to a point where the transistor will self distruct. While ever the car starts OK and the fault accures after a short time the ignition modules is OK. I understand that these ignition modules use the bulkhead of the car as a heat sink. If it were mine I would fit a different heat sink, but not so easy for anyone not used to handling these devices, the transistor metal cases have teflon or mica insulating pads and have 12+ and must not touch the body of the car.
I will check and see what MB do in these cases and report back shortly.

Malcolm

 

[Marc Taylor]

I think I have the same problem with my E200 (W124) as it starts ok but when you put it into P or N then revs to about 2000rpm for a few minutes before dropping down to around 800rpm. The Mercedes dealer told me it was the exhaust and manifold that was causing this problem but I have changes all those and the lambarda sensor and throttle countol unit but still not good. Did you get you ECU repaired and is you car working ok now?

 

[kth286]

guzzler

Is that the all electronic engine without distributor?

If so the ECU controls fuelling and ignition.

You need to get the codes read first and determine what error messages are present.

That will tell you what feedback sensor is out of spec and point out the likely fault.

Only go to a Merc specialist and get him to go through the readout with you.

It is highly UNLIKELY it is the ECU. More than 30% of ECU's sent for testing at a large repair organisation are NOT faulty, so there are some very suspect technicians out there - be careful who you deal with and get a recommendation in your local area.

If you e-mail Ben Cosgrave at "ben.cosgrave@******************.co.uk" and ask for a Merc specialist he should be able to point you in the right direction as he is a regional organiser in Ireland for the Mercedes-Benz club.

You may want to join the other club as well as you can meet like minded merc owners on a regular basis at a Dublin pub.

Hope this helps.

Regards

 

[gorselands]

Hi Guzzler,

came across this site for ECU's in Nottingham (a bit far from Dublin)

http://tunemycar.com/mercedes_common_ecu_failures.html

Thought it may be of interest as it refers to a problem merc.

Good luck

Mike

 

[Stevie A]

Does this E200 model have an over voltage protection relay???? Erratic idle, stalls, rough running, harder starts and erratic ABS light on, on other, slightly older Mercs are caused by faulty OVP relay. Cheaper to test than a new ECU too. Don't waste money on new ECU yet.

 

[Marc Taylor]

I have the same problem with unstable idling with my E200 and I was considering having the ECU tested and repaired. Although I was told today that if the ECU is the Siemens model (it is not coded) it is resin sealed and can be repaired so the only option would be to get a remanufactured ECU.

Marc

 

[Marc Taylor]

Hi,
Have you changed the fuel filter? My E200 had the same problem with uncontrolled idling but now I have changed the fuel filter the idling is back to normal.
It may not work with your problem but it is a lot cheaper than paying around £1200 for a new ECU from Mercedes or around £600 for a recon ECU.
Good Luck

Marc