Engine diagnostic indicator

[KentBenz]

Hi Merc owners,
My car is a 2000, E series elegance estate with the V6, 2.6l engine, has done 45K miles. 6 weeks ago the engine diagnostic indicator light came on. The only distinguishable problem when driving was a lumpy tick over. I took it into the local MB dealer who diagnosed an air mass flow sensor failure and also recommended new spark plugs. As the B service was nearly due I also had this done.
The car was returned; the warning light was off, though the lumpy tick-over, though reduced, was still present. 4weeks later the warning light came on and so I returned the car to the MB dealer. Their response was that the engine was OK but they thought both the CATS had failed mechanically!! The car was returned, the warning light was off, the lumpy tick-over was still present but the car drove perfectly well. I have had the CATS checked and they are OK. Yesterday the warning light again has appeared. I appreciate that faults latch the warning light and therefore can only assume any fault is transitory. Has any one experience of such problems or any thoughts on solutions.

 

[jberks]

You need to ask the dealer what the fault code is when the light comes on. This will indicate what the computer 'thinks' is the problem.

As far as lumpy tickover is concerned, I suspect you wasted your money on the plugs - my dealer recommended them last November at 45k too and I turned them down as she was running perfectly at the time. A few months ago at around 60k I started to get a slight jolt at tickover so figured that given their 60k lifespan this would be a good bet. I just replaced them myself and to be fair, they looked like they had some life in them yet. The idle improved slightly but still wasn't perfect and continued to get worse intermittently to the point that occasionally the whole car rocked.

What I have had problems with before however are the plug leads. The symptoms were very similar but I figured that as I had replaced them 3 years before they should be good for a while yet. I couldn't figure it and suspecting throttle housings or coil packs (which are beyond my ability) I gave it to the local specialist, he put another set of leads on and hey presto, shes back to perfect again!

The leads cost £250 and considering they start to degrade after only 2 1/2 years the charge is outrageous, but it did make a massive difference to my car on both occasions. Be aware, the dealer failed to diagnose the problem and it took the specialist a few days so it may be worth just telling them to change them.