C240 Lumpy Idle and Power Problems

[kamalpatel]

Hi everyone,

I have a 1999 C240 (V6) only 30k on the clock and am having some interesting problems. It had a B service and then started to have problems with power at any speed after the gearbox kicks down. The results would be lumpy idle and no power, but all was well after switching it off and then back on. Have been to an independent and have had the MAS and oxygen sensor diagnosed faulty/replaced and all went well for a while. I can't replicate the same problem now but on cold start in the last week it has had the same problem a couple of times but only at startup, it is not happening when kicking down or overtaking now and I can't repeat the problem like before. My independent is awaiting delivery of the star machine for a more in depth analysis. The report on it before was a misfire on cyl 4, 5 and 6.

I think this is appalling for a a car that has done less than 30k. Anyone had similar problems, and ideas, solutions??

Thx,
Kam

 

[jberks]

Hi,

My E240 suffered from lumpy idle. Turned out to corrosion inside the supressor caps. New leads and back to inperceptable tickover. (this was at 3 1/2 years old 25k miles and it took 6 visits and 3 days in the workshop to track down) Could explain your misfire. I also understand that t if the computer detects a bad misfire, it shuts down the injector to that cylinder to protect the cat. (I'm thinking cold+damp+corrosion=poor spark) Unfortunatly as there are 12 of them,prepare for a wallet transplant if it is. I didn't have a loss of power, but then I only had 1 bad one so it was only 1/12 down and the cylinder kept running. The specialist who fixed it, and the dealer previously had told me that the idle was normal and that they all do it. He only resolved it when I parked the car up and told him I didn't want it back until it was fixed, so I supect there are a lot of V6's out there with the same problem. Most mercs have highish mileage so people put the lumpy behaviour down to that, plus most people swap at 3 years so don't notice, and the next owner puts it down to being an 'old' car.

I've just had the MAS and o2 sensors replaced on mine. It seems that these components don't have a good lifespan. But it's not a merc thing, a lot of modern cars suffer from the same problems (Micras are notorious apparently). Allegedly, the MAS can sometimes be cleaned with brake cleaner which may solve the problem, but a £300 replacement is apparently easier !

 

[aclegg]

Lumpy idle

I also have an E240 with lumpy idle/power probs. Mercedes tell me that it was the hot film sensor.....but when I replaced this it made no difference. Now it needs to go back in to have the ecu told that we replaced this part. Don't have any faith that this will cure it though. Maybe I should replace the leads? Any idea how much this would cost?

 

[Arnie]

The suppressor caps are just a metal screen on the lead plug which covers the upper part of the spark-plug.

Just take off the spark-plug leads and look inside the cap and screen to see if you spot any corrosion, which might bridge the gap between the inner (live) contact and the metal (earth) screen. You can also spray in some WD-40 to displace any moisture if in doubt.

 

[jberks]

I do understand that the ECU has to be told about the change, so this may be it (needs calibrating or something). It cost me about £200-250 for a lead set, though this will have been full price so you could save on that.

 

[aclegg]

ECU looked at with no diference
my list of things to do next:
1. dirty throttle body
2. new leads/check for corrosion
3. fuel pump relay
4. mass & oxygen sensor
5. cold start valve
6. added by merc today.....maybe ignition coil pack....but this is a guess and will cost to figure out!!
any more suggestions from anyone?
:cry:

 

[kamalpatel]

C240 Solutions

I haven't had any further problems since I posted my problem and to date the MAS and Oxygen Sensor was replaced and are common candidate for these faults. I would pursue these first. I'd be interested to see what the solution is for you!

 

[jberks]

You've covered everything I can think of. These problems are a pain and to be honest, beyond the dealers capability. (didn't manage to resolve mine). As I said above, I found a good, reasonably priced local specialist, dropped that car off and told them to keep it as long as they needed (i had their loan corsa ). The bill wasn't too bad and they went through most of the things you suggest.
They swapped parts from other cars to test which saved me the cost of the throttle body which we suspected at one point, (put in, tested and then taken out again as it made no difference) something the dealer won't do, So you only pay for the labour, at half the price of the dealer, and if it isn't the cause, you're not left paying for a part you don't need (your hot film sensor?). You can tear your hair out chasing suspect after suspect, or just let them get on with it.
With compuer based cars like these, the maintenance cost is the part, plus time on the diagnostic computers, not the labour, so you don't same much doing it yourself. Plus, as you found with the film sensor, you still end up needing to visit the workshop as specialist computers are needed for calibration and resets.
Specialist are around £40-60 per hour against the dealers £90+ and my bill reflected their embarresment of not finding the fault sooner - (Id like to see a dealer even admit it, let alone reduce the labour charge accordingly).

Also, I thought the hot film sensor was the Air Mass Sensor ? If so, I guess symptoms vary but when mine went, I was left with so little power, it would just manage 50mph flat out with a 0-30 of about 30 seconds, and the failure occurred amost instantly.