W203 / 2001 C240 Auto Running Problems..

[proteo]

My merc has a strange issue it started like this.. One day the wife was driving (the first mistake) and she called me to say it was running very strangely and a warning symbol had appeared on the dashboard.

Turns out the computer found some ignition fault (naturally 2months after a 'B' Service). I took it to my local specialist who changed 2 leads (admittedly instead of the complete set as he wanted to save me some money) this resolved the fault but the engine still wasn't running quite right. He next changed all 12 platinum plugs and that really improved things. When you drive it normally (without a lead foot on the accelerator) its fine, however the car still has two problems:

1. When you reach a traffic light or roundabout sometimes it starts to shake, if you put your foot on the gas too quickly it will:
a. go no where
b. stall

2. The second problem is if you try to accelerate quickly i.e. kick down it will not co-operate at all, you have to accelerate smoothly for it to pick up speed else it just freezes.

I took the car to an auto-electrian and here's what he did:

1. Tried a new MAF but that made no difference.
2. Tested the air sensor / oxygen sensor that was ok too.

His conclusion was that the fault is now either with the Catalytic Convertor or Gearbox. He told me its not ignition related else it would run rough all the time. His last suggestion was to disconnect the front pipe and take it for a spin to rule out the cat. The computer unfortunately shows no faults at all any more which doesn't help at all.

Needless to say I've already spent a lot of time and money on this issue.

Would appreciate if anyone else has had a similar issues or can provide any insight. Its now due for an 'A' service and I will ask the garage to try disconnecting the CAT as there isn't a lot else to test.

 

[jberks]

You say the problem is intermittent
So, when it's running rough, if you switch off and back on again - does that improve things? - I'm trying to establish whether it's going into safe mode or not.
Leads will cause poor idling but as it's twin spark - generally not poor running - that's my experience of that engine anyway. If the gearbox is simply refusing to kick down, then that's not a gearbox problem but it is a safe mode problem. Also gentle acceleration=ok, heavier and it plays up - all point back to MAF.
I guess a weak fuel pump would have a similar effect though - but not at idle. I'd revisit the MAF with your specialist.

I have heard of poor idling etc with the throttle actuator too, but again, it shouldn't effect kick down.

 

[mercdriver]

I've just read on an american site about similar problems. It seems one common demominator was a brake light failure. Some were reporting a fault indicated on the dash, but only intermittent. The car thinks it is braking, therefore will not accelerate. Drivers following cars have said that brake lights were flashing on and off, but this was only happening intermittently and not very often. Have you had any brake light problems? Apparently, if you press both pedals at the same time, you won't get any power.

Cheers

Mark

 

[hs500]

ok, my problem might be a different one ... but the symptoms look pretty much the same. In fact just got back from a computer diagnosis of my C180 203 2001 today and the tech reported that the computer showed a fault in the ACCELERATOR PEDAL LIMIT SENSOR, and he said that it was a fairly simple thing to replace and this would cure the problem. The problem with my C180 is that when i step on the accelerator, the car moves but only after 5 seconds, but once taken off it runs okayish, well very much underpower but runs. Iv already had a change of the mass airflow sensor but that made no difference, well actually it did, to my credit card account :-(